[OCI] Cache Login credentials

[souleb]

This PR add caching to Login function for each Provider.

Depends on #766

[stefanprodan]

This looks great, thanks!

PS. The cache pkg branch is behind main and has old Kubernetes deps. Do you want to merge this into the cache-athn branch and rebase there?

[darkowlzz]

We can test this in integration test by updating the test app and setting a cache instance in the ProviderOptions in https://github.com/fluxcd/pkg/blob/oci/v0.37.1/oci/tests/integration/testapp/main.go#L50.

[souleb]

I have triggered the integration tests on gcp: https://github.com/fluxcd/pkg/actions/runs/9561954422

[darkowlzz]

Thanks for adding the cache to the integration test.
Because the test app runs in the cluster in a separate pod and the test runner runs outside of the cluster, we don't have a nice way to also test the use of data in the cache. The test app can be updated to test this specific scenario to perform another login and check the obtained credential with the previous one. But I guess that's not needed as we test the same in unit tests.

[darkowlzz]

LGTM!