Add integration tests for OIDC endpoints

[hectorcast-db]

Summary

• Adds integration tests for OIDC endpoint resolution across workspace, UC workspace, account, and UC account environments
• Includes unified host endpoint tests gated on UNIFIED_HOST environment variable for account contexts

Test plan

• CI passes
• Integration tests run successfully in workspace, ucws, account, and ucacct environments
• Unified host tests are skipped when UNIFIED_HOST is not set

This pull request was AI-assisted by Isaac.

[github-actions]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger:
go/deco-tests-run/sdk-java

Inputs:

• PR number: 755
• Commit SHA: dbeb33d868e4c3433de712670d54dd2efab4f3a1

Checks will be approved automatically on success.

[github-actions]

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