Feat: add new plugin for metrics

[VivekPipaliya23]

Proposed Changes

This PR will add a new verneMQ plugin named vmq_metrics_plus for metrics and observability instrumentations. Topic-level metrics are moved in this new plugin.

Types of Changes

• Bugfix (non-breaking change which fixes issue #XXXX)
• 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, styles...)
• DevOps (Build scripts, pipelines...)

Checklist

• I have read the CODE_OF_CONDUCT.md document
• 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 needed)
• Any dependent changes have been merged and published in related repositories
• I have updated changelog (At the bottom of the release version)
• I have squashed all my commits into one before merging

[dhruvjain99]

Please make sure your pipeline passes. And then only make the PR ready to be reviewed. In all other cases keep it WIP.