Re:433 Expose SQS ReceiptHandle in task signature

[bharat-p]

Fixes #433

When using SQS broker there is no way to get hold of SQS message's ReceiptHandle, this PR adds a new property SQSReceiptHandle to tasks.Signature which gets populated by SQS broker when consuming a message

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@4c148cb). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master     #434   +/-   ##
=========================================
  Coverage          ?   47.93%           
=========================================
  Files             ?       29           
  Lines             ?     2643           
  Branches          ?        0           
=========================================
  Hits              ?     1267           
  Misses            ?     1237           
  Partials          ?      139

Impacted Files	Coverage Δ
v1/tasks/signature.go	41.17% <ø> (ø)
v1/brokers/sqs/sqs.go	51.36% <100%> (ø)

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[bharat-p]

@RichardKnop after merging this PR, please also tag new version so it can be referenced by go.mod

[bharat-p]

@RichardKnop can you please merge this