Make client auth extension public and implement component.Component

[damemi]

Working on contributing this upstream (open-telemetry/opentelemetry-collector-contrib#31518), we will need to export some of the functions like CreateExtension and CreateDefaultConfig. This also implements the component.Component interface so the extension can be created without calling google.FindDefaultCredentials(), which can result in an immediate error if the credentials are not found. This enables lifecycle tests upstream.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 60.07%. Comparing base (e16634a) to head (842371d).
Report is 4 commits behind head on main.

Files	Patch %	Lines
extension/googleclientauthextension/factory.go	80.00%	3 Missing ⚠️
extension/googleclientauthextension/grpc.go	57.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #814      +/-   ##
==========================================
+ Coverage   59.79%   60.07%   +0.28%     
==========================================
  Files          56       56              
  Lines        5743     5896     +153     
==========================================
+ Hits         3434     3542     +108     
- Misses       2159     2202      +43     
- Partials      150      152       +2     

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[dashpole]

Given how small this library is, should the entire thing just live upstream?

[damemi]

Given how small this library is, should the entire thing just live upstream?

I'm thinking it's best to do it the same way we do with our exporters, where the code lives downstream so we have more control over testing and updates. We can always follow up with moving the rest of the code upstream if we want.

[damemi]

@dashpole updated this like we talked about offline, ready for review now