CI: Add a workflow to add a git tag via web UI

[leofang]

Today before triggering the release workflow we need to create a git tag locally and push it to the remote repo, because

1. GitHub for whatever reason does not offer a way for us to do this in the browser
2. our release workflow needs the tag to reverse-lookup the corresponding run ID: https://github.com/NVIDIA/cuda-python/blob/36b8c5fa799ddd9b8c9eb8b4816258485cbeeb7c/.github/workflows/release.yml#L22-L25

However, this mixed workflow is error prone and we did accidentally pushed wrong tags in the past. We should avoid this by adding a workflow to tag (based on the commit). Then, we can consider combine this new workflow with the release workflow, so that we don't need to provide both commit and tag; just the former should be enough for everything.