Auto-subscribe user to repository when they commit/tag to it (#7657)

* Add support for AUTO_WATCH_ON_CHANGES and AUTO_WATCH_ON_CLONE

* Update models/repo_watch.go

Co-Authored-By: Lauris BH <lauris@nix.lv>

* Round up changes suggested by lafriks

* Added changes suggested from automated tests

* Updated deleteUser to take RepoWatchModeDont into account, corrected inverted DefaultWatchOnClone and DefaultWatchOnChanges behaviour, updated and added tests.

* Reinsert import "github.com/Unknwon/com" on http.go

* Add migration for new column `watch`.`mode`

* Remove serv code

* Remove WATCH_ON_CLONE; use hooks, add integrations

* Renamed watch_test.go to repo_watch_test.go

* Correct fmt

* Add missing EOL

* Correct name of test function

* Reword cheat and ini descriptions

* Add update to migration to ensure column value

* Clarify comment

Co-Authored-By: zeripath <art27@cantab.net>

* Simplify if condition

models/migrations/v106.go

@@ -0,0 +1,26 @@
+// Copyright 2019 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 (
+	"xorm.io/xorm"
+)
+
+// RepoWatchMode specifies what kind of watch the user has on a repository
+type RepoWatchMode int8
+
+// Watch is connection request for receiving repository notification.
+type Watch struct {
+	ID   int64         `xorm:"pk autoincr"`
+	Mode RepoWatchMode `xorm:"SMALLINT NOT NULL DEFAULT 1"`
+}
+
+func addModeColumnToWatch(x *xorm.Engine) (err error) {
+	if err = x.Sync2(new(Watch)); err != nil {
+		return
+	}
+	_, err = x.Exec("UPDATE `watch` SET `mode` = 1")
+	return err
+}