Frontend metrics configuration handling

[namannandan]

Description

Implementation of frontend metrics configuration parsing and validation.
Design: #1492

Fixes #2134

Type of change

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

Feature/Issue validation/testing

• Unit tests included with PR run as part of sanity test

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 #2190 (d9ace25) into master (dd8e792) will decrease coverage by 0.09%.
The diff coverage is n/a.

❗ Current head d9ace25 differs from pull request most recent head 9970acc. Consider uploading reports for the commit 9970acc to get more accurate results

@@            Coverage Diff             @@
##           master    #2190      +/-   ##
==========================================
- Coverage   71.47%   71.38%   -0.09%     
==========================================
  Files          73       73              
  Lines        3341     3341              
  Branches       57       57              
==========================================
- Hits         2388     2385       -3     
- Misses        950      953       +3     
  Partials        3        3              

see 1 file with indirect coverage changes

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[lxning]

TsMetrics and ModelMetrics are exactly same. it is not necessary to have them.

Only need:

• MetricConfiguraiton.java
• MetricSpec.java

[namannandan]

Addressed review comments:

• Consolidated TsMetrics and ModelMetrics into a single class MetricTypes to avoid code duplication.
• Removed YAMLMetricsConfigurationHandler and moved configuration loader function into MetricConfiguration class.
• Added support for metrics mode configuration environment variable.