Distinguish nack metrics by requeue flag

[ohksj77]

Proposed Changes

• Enhanced the MetricsCollector to distinguish metrics for NACK with requeue option
• Related issue: Enhance the MetricsCollector to distinguish metrics for NACK (requeue = true) vs NACK (requeue = false) #1442

Types of Changes

• Bugfix (non-breaking change which fixes issue #NNNN)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (correction or otherwise)
• Cosmetics (whitespace, appearance)

Checklist

• I have read the CONTRIBUTING.md document
• I have signed the CA (see https://cla.pivotal.io/sign/rabbitmq)
• All tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in related repositories

[acogoluegnes]

Thanks for this contribution. I edited some minor details but it created another PR. I will close this PR and you are welcome to follow up on #1476.

[ohksj77]

Thanks for this contribution. I edited some minor details but it created another PR. I will close this PR and you are welcome to follow up on #1476.

Thank you for adding to my PR needs. 😄