- Introduces the `RDIFF_ACCEPT_NEW_GOLDENS` commit message tag.
- Conditionally skip the `test-renderdiff` presubmit comparison
if this tag is present.
- Extracts renderdiff generation into a reusable
`.github/actions/renderdiff-generate` composite action.
- Modifies `postsubmit-main.yml` to automatically generate new
goldens and push them to a temporary
`accept-goldens-<short-hash>` branch before merging them into
`main` when the tag is found.
