Add gRPC authenticator for exporter

[saxocellphone]

Adding missing gRPC authentication features to the experimental Authenticator api. Closes #6953

[linux-foundation-easycla]

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• ✅ login: saxocellphone (8713eed)

[codecov]

Codecov Report

Attention: Patch coverage is 48.00000% with 13 lines in your changes missing coverage. Please review.

Project coverage is 90.06%. Comparing base (e3cfede) to head (8713eed).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
...orter/sender/okhttp/internal/OkHttpGrpcSender.java	10.00%	8 Missing and 1 partial ⚠️
...edchannel/internal/UpstreamGrpcSenderProvider.java	63.63%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6952      +/-   ##
============================================
- Coverage     90.09%   90.06%   -0.03%     
- Complexity     6601     6603       +2     
============================================
  Files           730      730              
  Lines         19843    19864      +21     
  Branches       1955     1958       +3     
============================================
+ Hits          17877    17890      +13     
- Misses         1371     1379       +8     
  Partials        595      595              

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[saxocellphone]

I was trying to figure out why the build-graal check is failing. It's complaining about changing a static variable in io.opentelemetry.exporter.internal.auth.Authenticator. Which is WAI. Is the test flaky?

EDIT: fixed by adding the following to resources/META-INF/native-image/io.opentelemetry.opentelemetry-exporter-common/reflect-config.json

  {
    "name":"io.opentelemetry.exporter.internal.auth.Authenticator",
    "queryAllDeclaredMethods":true
  }