docs(github): correct action token configuration

[neriousy]

Summary

• remove the stale legacy token documentation and never-valid github_token example from V2
• document the current mentions, variant, oidc_base_url, and use_github_token inputs
• show a complete caller-token configuration and clarify that OIDC permission is unnecessary in that mode
• fix the malformed indentation in the manual workflow example

This is the V2 companion to #44793. The composite action and GitHub documentation are present on both branches even though the legacy handler implementation is not part of V2.

Thanks @harshil-mistry for identifying the stale input documentation in #44668.

Verification

• Prettier
• git diff --check
• full V2 workspace typecheck from the pre-push hook (32/32 tasks)

Related to #44667