fix: Update ResourceMetrics public API

[utpilla]

Changes

• Update public APIs for Resource Metrics

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 27 lines in your changes missing coverage. Please review.

Project coverage is 81.4%. Comparing base (82e5ed4) to head (1af8306).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-sdk/src/metrics/data/mod.rs	0.0%	15 Missing ⚠️
opentelemetry-stdout/src/metrics/exporter.rs	0.0%	9 Missing ⚠️
opentelemetry-proto/src/transform/metrics.rs	0.0%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2965     +/-   ##
=======================================
- Coverage   81.5%   81.4%   -0.1%     
=======================================
  Files        126     126             
  Lines      24303   24319     +16     
=======================================
- Hits       19816   19812      -4     
- Misses      4487    4507     +20     

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[cijothomas]

Awesome!