This upgrades `tibdex/github-app-token` to `v2` and
`google-github-actions/release-please-action` to `v4`.
Among other things, this ensures that we are compatible with the GitHub
Actions upgrade to Node 20, and avoiding issues when Node 16-based
actions are deprecated sometime this spring.
BREAKING CHANGE: Underlying actions have been upgraded, requiring changes to available inputs
Brings this action more inline with the upstream action, by keeping the
config and manifest filenames identical, and simply moving them into the
".github" directory.
BREAKING CHANGE: Change default manifest path to `.github/.release-please-manifest.json`.