Prometheus label conversion refactored to align with spec

[onurkybsi]

Resolves the issue #5987.

[codecov]

Codecov Report

Attention: Patch coverage is 84.61538% with 6 lines in your changes missing coverage. Please review.

Project coverage is 89.78%. Comparing base (29523e6) to head (44b28c8).
Report is 42 commits behind head on main.

Files with missing lines	Patch %	Lines
.../exporter/prometheus/Otel2PrometheusConverter.java	84.61%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7291      +/-   ##
============================================
- Coverage     90.03%   89.78%   -0.25%     
- Complexity     6915     6969      +54     
============================================
  Files           787      795       +8     
  Lines         20864    21122     +258     
  Branches       2023     2056      +33     
============================================
+ Hits          18784    18965     +181     
- Misses         1441     1497      +56     
- Partials        639      660      +21     

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