ci(release): automate signed release tags and release notes (#39544)

Automate release tagging as proposed in
https://github.com/go-gitea/gitea/pull/39544#issuecomment-5955939142,
part of https://github.com/go-gitea/gitea/issues/39550.

A maintainer selects a release branch and version in the
`release-create-tag` workflow. After approval through the
`release-signing` environment, it pushes a GPG-signed tag. The tag
starts the existing release build, which generates GitHub release notes
with git-cliff from commits since the previous release, skipping `chore`
and `ci` commits.

`CHANGELOG.md` and release-candidate releases are removed. The workflow
reuses the existing `GPGSIGN_KEY`, `GPGSIGN_PASSPHRASE`, and
`RELEASE_TOKEN` repository secrets.


Closes https://github.com/go-gitea/gitea/issues/39550

---------

Co-authored-by: bircni <bircni@users.noreply.github.com>
Co-authored-by: silverwind <me@silverwind.io>

cliff.toml

@@ -0,0 +1,10 @@
+[git]
+commit_parsers = [
+  { message = "^(chore|ci)(\\([\\w/.-]+\\))?!?: ", skip = true },
+  { message = "^feat", group = "Features" },
+  { message = "^enhance", group = "Enhancements" },
+  { message = "^perf", group = "Performance" },
+  { message = "^fix", group = "Bug Fixes" },
+  { message = "^docs", group = "Documentation" },
+  { message = ".*", group = "Miscellaneous" },
+]