Add GitHubIdentityProvider and support browser-based auth in the Pinniped Supervisor

[cfryanr]

This feature was originally developed on a long-lived feature branch with its own CI pipeline, but now should be ready to merge that whole feature branch to main.

Release note:

Add GitHubIdentityProvider and support browser-based auth in the Pinniped Supervisor.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 72.74336% with 308 lines in your changes missing coverage. Please review.

Project coverage is 30.61%. Comparing base (16c8911) to head (6b64a8a).

Files	Patch %	Lines
...ioned/typed/idp/v1alpha1/githubidentityprovider.go	0.00%	107 Missing :warning:
...s/supervisor/idp/v1alpha1/zz_generated.deepcopy.go	63.39%	53 Missing and 3 partials :warning:
...d/idp/v1alpha1/fake/fake_githubidentityprovider.go	32.39%	46 Missing and 2 partials :warning:
internal/controller/utils.go	0.00%	27 Missing :warning:
...vedprovider/resolvedoidc/resolved_oidc_provider.go	4.54%	21 Missing :warning:
...g/githubupstreamwatcher/github_upstream_watcher.go	97.00%	7 Missing and 3 partials :warning:
...nalversions/idp/v1alpha1/githubidentityprovider.go	61.90%	6 Missing and 2 partials :warning:
...sor/listers/idp/v1alpha1/githubidentityprovider.go	65.21%	7 Missing and 1 partial :warning:
internal/githubclient/githubclient.go	95.80%	4 Missing and 2 partials :warning:
...rovider/resolvedgithub/resolved_github_provider.go	94.79%	4 Missing and 1 partial :warning:
... and 5 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1978 +/- ## ========================================== + Coverage 29.61% 30.61% +0.99% ========================================== Files 350 363 +13 Lines 58750 60481 +1731 ========================================== + Hits 17398 18514 +1116 - Misses 40834 41432 +598 - Partials 518 535 +17 ```

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