in_tail: Add throttling metrics

[Athishpranav2003]

Which issue(s) this PR fixes:
Fixes #
fluent/fluent-plugin-prometheus#190

What this PR does / why we need it:
It adds metrics to the throttling of logs while taling logs using in_tail plugin as asked in the above issue.
Once this PR is accepted corresponding changes in prometheus plugin will be made to expose the newly added throttling metric
Docs Changes:
Need docs change in prometheus plugin for metrics description
Release Note:
NA

[Athishpranav2003]

@ashie Please take a look at this. I am not sure which sort of metric is important here. Once this is merged and released i will add the changes to prometheus plugin too, I will create the PR for it too in some time

[Athishpranav2003]

@ashie can you approve the checks?

[ashie]

Here is a reply for your comment you seem deleted already:

i cant run the checks locally because its too heavy

Yes, fluentd takes too long time to run whole tests.
e.g.) It takes 1035 seconds in https://github.com/fluent/fluentd/actions/runs/9925766505/job/27418533059

So even we fluentd maintainers also don't often run all tests locally.
Instead, run only partial tests related with the change.

e.g.) Run only in_tail's multiline related tests, and show test names currently running (-v option).

$ bundle exec rake test TEST=test/plugin/test_in_tail.rb TESTOPTS="-v --testcase=\"TailInputTest::multiline\""

You can see the explanation of test options by the following command:

$ bundle exe rake test TESTOPTS="--help"
...
Usage: /home/aho/Projects/Fluentd/fluentd/vendor/bundle/ruby/3.2.0/gems/rake-13.2.1/lib/rake/rake_test_loader.rb [options] [-- untouched arguments]
    -r, --runner=RUNNER              Use the given RUNNER.
                                     (c[onsole], e[macs], x[ml])
        --collector=COLLECTOR        Use the given COLLECTOR.
                                     (de[scendant], di[r], l[oad], o[bject]_space)
    -n, --name=NAME                  Runs tests matching NAME.
                                     Use '/PATTERN/' for NAME to use regular expression.
                                     Regular expression accepts options.
                                     Example: '/taRget/i' matches 'target' and 'TARGET'
        --ignore-name=NAME           Ignores tests matching NAME.
                                     Use '/PATTERN/' for NAME to use regular expression.
                                     Regular expression accepts options.
                                     Example: '/taRget/i' matches 'target' and 'TARGET'
    -t, --testcase=TESTCASE          Runs tests in TestCases matching TESTCASE.
                                     Use '/PATTERN/' for TESTCASE to use regular expression.
                                     Regular expression accepts options.
                                     Example: '/taRget/i' matches 'target' and 'TARGET'
        --ignore-testcase=TESTCASE   Ignores tests in TestCases matching TESTCASE.
                                     Use '/PATTERN/' for TESTCASE to use regular expression.
                                     Regular expression accepts options.
                                     Example: '/taRget/i' matches 'target' and 'TARGET'
        --location=LOCATION          Runs tests that defined in LOCATION.
                                     LOCATION is one of PATH:LINE, PATH or LINE.
        --attribute=EXPRESSION       Runs tests that matches EXPRESSION.
                                     EXPRESSION is evaluated as Ruby's expression.
                                     Test attribute name can be used with no receiver in EXPRESSION.
                                     EXPRESSION examples:
                                       !slow
                                       tag == 'important' and !slow
        --[no-]priority-mode         Runs some tests based on their priority.
        --default-priority=PRIORITY  Uses PRIORITY as default priority
                                     (h[igh], i[mportant], l[ow], m[ust], ne[ver], no[rmal])
    -I, --load-path=DIR[:DIR...]     Appends directory list to $LOAD_PATH.
        --color-scheme=SCHEME        Use SCHEME as color scheme.
                                     (d[efault])
        --config=FILE                Use YAML format FILE content as configuration file.
        --order=ORDER                Run tests in a test case in ORDER order.
                                     (a[lphabetic], d[efined], r[andom])
        --max-diff-target-string-size=SIZE
                                     Shows diff if both expected result string size and actual result string size are less than or equal SIZE in bytes.
                                     (1000)
        --[no-]stop-on-failure       Stops immediately on the first non success test
                                     (false)
        --[no-]debug-on-failure      Run debugger if available on failure
                                     (false)
        --[no-]gc-stress             Enable GC.stress only while each test is running
                                     (false)
    -v, --verbose=[LEVEL]            Set the output level (default is normal).
                                     (i[mportant-only], n[ormal], p[rogress], s[ilent], v[erbose])
        --[no-]use-color=[auto]      Uses color output
                                     (default is auto)
        --progress-row-max=MAX       Uses MAX as max terminal width for progress mark
                                     (default is auto)
        --progress-style=STYLE       Uses STYLE as progress style
                                     (f[ault-only], i[nplace], m[ark]
        --no-show-detail-immediately Shows not passed test details immediately.
                                     (default is yes)
        --[no-]reverse-output        Shows fault details in reverse.
                                     (default is yes for tty output, no otherwise)
        --output-file-descriptor=FD  Outputs to file descriptor FD
        --                           Stop processing options so that the
                                     remaining options will be passed to the
                                     test.
    -h, --help                       Display this help.

Deprecated options:
        --console                    Console runner (use --runner).

[ashie]

Thanks for your work.
It looks good.
I commented on one thing that needs to be fixed.

[Athishpranav2003]

@ashie addressed the comments

[ashie]

LGTM

Although It would be better to add tests for it, we don't have tests for metrics originally. So I don't always require adding them in this pull request. Let's tackle on it in other pull request(s).

I'll wait merging this until tomorrow to see if other maintainers have comments.

[ashie]

I'll wait merging this until tomorrow to see if other maintainers have comments.

(And waiting CI)

[cosmo0920]

Looks attractive. Thanks!

[ashie]

Thanks!