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

modules/appstate/appstate_test.go

@@ -0,0 +1,64 @@
+// 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 appstate
+
+import (
+	"path/filepath"
+	"testing"
+
+	"code.gitea.io/gitea/models/db"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMain(m *testing.M) {
+	db.MainTest(m, filepath.Join("..", ".."), "")
+}
+
+type testItem1 struct {
+	Val1 string
+	Val2 int
+}
+
+func (*testItem1) Name() string {
+	return "test-item1"
+}
+
+type testItem2 struct {
+	K string
+}
+
+func (*testItem2) Name() string {
+	return "test-item2"
+}
+
+func TestAppStateDB(t *testing.T) {
+	assert.NoError(t, db.PrepareTestDatabase())
+
+	as := &DBStore{}
+
+	item1 := new(testItem1)
+	assert.NoError(t, as.Get(item1))
+	assert.Equal(t, "", item1.Val1)
+	assert.EqualValues(t, 0, item1.Val2)
+
+	item1 = new(testItem1)
+	item1.Val1 = "a"
+	item1.Val2 = 2
+	assert.NoError(t, as.Set(item1))
+
+	item2 := new(testItem2)
+	item2.K = "V"
+	assert.NoError(t, as.Set(item2))
+
+	item1 = new(testItem1)
+	assert.NoError(t, as.Get(item1))
+	assert.Equal(t, "a", item1.Val1)
+	assert.EqualValues(t, 2, item1.Val2)
+
+	item2 = new(testItem2)
+	assert.NoError(t, as.Get(item2))
+	assert.Equal(t, "V", item2.K)
+}