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/fixtures/repository.yml

@@ -10,7 +10,7 @@
   num_closed_pulls: 0
   num_milestones: 3
   num_closed_milestones: 1
-  num_watches: 3
+  num_watches: 4
   status: 0
 
 -

models/fixtures/watch.yml

@@ -2,13 +2,28 @@
   id: 1
   user_id: 1
   repo_id: 1
+  mode: 1 # normal
 
 -
   id: 2
   user_id: 4
   repo_id: 1
+  mode: 1 # normal
 
 -
   id: 3
   user_id: 9
   repo_id: 1
+  mode: 1 # normal
+
+-
+  id: 4
+  user_id: 8
+  repo_id: 1
+  mode: 2 # don't watch
+
+-
+  id: 5
+  user_id: 11
+  repo_id: 1
+  mode: 3 # auto