Replace deprecated `tibdex/github-app-token` action with the
new and official `actions/create-github-app-token` action.
This required removing numerous token related inputs for the action, as
the new action does not support the same sets of inputs.
BREAKING CHANGE: Removed various app token related inputs not available
in new underlying action. Please see updated list of inputs in README.
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`.
