Update public client library for Cloud Monitoring to introduce new Uptime check feature.

Uptime HTTP(S) checks can now be GET or POST.

PiperOrigin-RevId: 306855444

Source-Author: Google APIs <noreply@google.com>
Source-Date: Thu Apr 16 08:56:29 2020 -0700
Source-Repo: googleapis/googleapis
Source-Sha: 101d31acd73076c52d78e18322be01f3debe8cb5
Source-Link: googleapis/googleapis@101d31a

Author: yoshi-automation