Frontend IMetrics, LogMetric and PrometheusMetric

[lxning]

Description

Implementation of frontend metrics helper classes for LogMetric and PrometheusMetric

Design: #1492

Fixes #2139

Type of change

• New feature (non-breaking change which adds functionality)

Feature/Issue validation/testing

Unit tests included in this PR

Checklist:

• Did you have fun?
• Have you added tests that prove your fix is effective or that this feature works?
• Has code been commented, particularly in hard-to-understand areas?
• Have you made corresponding changes to the documentation?

[codecov]

Codecov Report

Merging #2165 (c7310b3) into master (4ea172d) will not change coverage.
The diff coverage is n/a.

❗ Current head c7310b3 differs from pull request most recent head 234ca97. Consider uploading reports for the commit 234ca97 to get more accurate results

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[lxning]

LGTM now.

[namannandan]

Approving on @lxning behalf based on the above comment.

[agunapal]

@lxning Could you please update the appropriate README files for the additional metrics we are collecting.
Also, from. a user point of view, do they have to enable some config to get these metrics?

[namannandan]

@agunapal Currently there aren't any new metrics that are going to be collected. The existing metrics are being migrated to a new implementation that supports two modes, i.e log and prometheus. A configuration file is used specify all the metrics that will be collected, which was updated in this PR: #2164
The final PR for the metrics frontend implementation will include necessary documentation for the prometheus mode: #2199

The default mode will be log mode, which follows the exact same logging format used currently. To enable prometheus mode, a config option has been added. Details are in this PR: #2190

This PR implements the necessary helper classes for the frontend metrics implementation refactoring.