Gitea writes its own AppPath into git hook scripts. If Gitea's AppPath changes, then the git push will fail.
This PR:
* Introduce an AppState module, it can persist app states into database
* During GlobalInit, Gitea will check if the current AppPath is the same as last one. If they don't match, Gitea will sync git hooks.
* Refactor some code to make them more clear.
* Also, "Detect if gitea binary's name changed" #11341 is related, we call models.RewriteAllPublicKeys to update ssh authorized_keys file
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