[feature] Release workflow: automatically publish tag and release

Follow up of #496.

We could add a github action which detects the commit message generated by the releaser tool and automatically push a git tag and publish a release. This would help further automating the release workflow, which now needs the review and approval of a maintainer, while another maintainer needs to keep the release flow open waiting for the PR to get merged, which may not happen while the maintainer is still around.

We also need to modify the releaser tool to play well with this case, I guess it should be able to go straight to the git tag part and release part. Not sure what we can do with the signature, I guess I can create a new signature and make it available as an organization secret.

Start with #496 and the existing release workflow and releaser tool; no file paths or tests are named. Define how the workflow detects the releaser-generated commit, then verify the intended outcome: a git tag and published release without maintainer intervention, including a decided approach to the signing secret.