Add option to run benchmarks on PRs

[trask]

I have a couple of PRs where this would be helpful.

Initially I combined it into the existing benchmark.yml but it just ended up being if conditions everywhere, so prefer them separate in the end.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (f3c8886) to head (c3e1f60).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7698   +/-   ##
=========================================
  Coverage     90.12%   90.12%           
  Complexity     7187     7187           
=========================================
  Files           814      814           
  Lines         21700    21700           
  Branches       2123     2123           
=========================================
  Hits          19557    19557           
  Misses         1477     1477           
  Partials        666      666           

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[trask]

this is the list from

opentelemetry-java/.github/workflows/benchmark.yml

Line 46 in 1e763b2

java -jar libs/opentelemetry-sdk-trace-*-jmh.jar -rf json SpanBenchmark SpanPipelineBenchmark ExporterBenchmark

[zeitlinger]

this is the third benchmark workflow

would it be possible to use the "reusable pattern" or alternatively use a script?