Move database settings from models to setting (#7806)

* move database settings from models to setting

* update docs

* fix checkout pr

* fix tests

* fix lint

* remove unsupported tidb options

* correct wrong variable name

* remove tidb totally

modules/setting/database_sqlite.go

@@ -0,0 +1,16 @@
+// +build sqlite
+
+// Copyright 2014 The Gogs 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 setting
+
+import (
+	_ "github.com/mattn/go-sqlite3"
+)
+
+func init() {
+	EnableSQLite3 = true
+	SupportedDatabases = append(SupportedDatabases, "SQLite3")
+}