Inspired by
https://github.com/go-gitea/gitea/pull/24530#issuecomment-1558815301
This PR use a file filter action to do different CI jobs according
changed files types. All types are defined in
`.github/file-filters.yml`. Now there are 4 types, `docs`, `backend`,
`frontend` and `build`. Then if a PR only changed docs files, those CI
jobs which passed the conditions will run, and other types are also like
this.
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Co-authored-by: silverwind <me@silverwind.io>
