Docs: Update Windows-specific guidance for running Prometheus exporter test

[Annosha]

Referencing the issue noted here JApiCmp Failure in setting up opentelemetry-java locally, it would be beneficial for beginner contributors to include guidance on handling Prometheus test failures on Windows, along with an alternative command. This addition will help new contributors navigate the setup process more smoothly and contribute effectively to the repository.
@trask @shalk

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.49%. Comparing base (b1cd30e) to head (0c77be6).
Report is 20 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6823      +/-   ##
============================================
+ Coverage     90.12%   90.49%   +0.37%     
- Complexity     6546     6599      +53     
============================================
  Files           728      731       +3     
  Lines         19702    19735      +33     
  Branches       1935     1935              
============================================
+ Hits          17756    17859     +103     
+ Misses         1347     1285      -62     
+ Partials        599      591       -8     

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[trask]

hi @Annosha! I'm giving it a try to instead fix the tests on Windows (and keep them fixed by running them in CI), see #6824