Sync gitea app path for git hooks and authorized keys when starting (#17335)

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

models/migrations/migrations.go

@@ -352,6 +352,8 @@ var migrations = []Migration{
 	NewMigration("Add issue content history table", addTableIssueContentHistory),
 	// v199 -> v200
 	NewMigration("Add remote version table", addRemoteVersionTable),
+	// v200 -> v201
+	NewMigration("Add table app_state", addTableAppState),
 }
 
 // GetCurrentDBVersion returns the current db version

models/migrations/v200.go

@@ -0,0 +1,23 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"fmt"
+
+	"xorm.io/xorm"
+)
+
+func addTableAppState(x *xorm.Engine) error {
+	type AppState struct {
+		ID       string `xorm:"pk varchar(200)"`
+		Revision int64
+		Content  string `xorm:"LONGTEXT"`
+	}
+	if err := x.Sync2(new(AppState)); err != nil {
+		return fmt.Errorf("Sync2: %v", err)
+	}
+	return nil
+}