Add nudge to PR actions

[theletterf]

This PR adds a /nudge action that relies on gh run rerun: https://cli.github.com/manual/gh_run_rerun

The idea is addressing the need for rerunning checks after a /fix command. I wonder if adding this command at the end of all fix commands could also solve the situation.

Might potentially fix #4339

[chalin]

Cool! ✨

Have you tested this locally? I did, and the rerun request doesn't seem to be doing anything in GH (see inline comment for details):

$ gh run rerun $RUNID                                                                                                                    
✓ Requested rerun of run 13966456806

Edit: reruns seem to get created, but they (1) don't seem to be picking up the latest commits to the branch; (2) the status of the rerun checks don't appear on the PR itself.

[theletterf]

/fix:format

[opentelemetrybot]

You triggered fix:format action run at https://github.com/open-telemetry/opentelemetry.io/actions/runs/13969072963

[opentelemetrybot]

fix:format failed or was cancelled. For details, see https://github.com/open-telemetry/opentelemetry.io/actions/runs/13969072963.

[theletterf]

@chalin I reviewed the action and went for a simpler approach, that is, creating and pushing an empty commit on demand. As we squash commits when merging PRs, this adds no noise to the git history of main and avoids complex checks-checking logic.