Add config options to hide issue events (#17414)

* Add config option to hide issue events
Adds a config option `HIDE_ISSUE_EVENTS` to hide most issue events (changed labels, milestones, projects...) on the issue detail page.
If this is true, only the following events (comment types) are shown:
* plain comments
* closed/reopned/merged
* reviews

* Make configurable using a list

* Add docs

* Add missing newline

* Fix merge issues

* Allow changes per user settings

* Fix lint

* Rm old docs

* Apply suggestions from code review

* Use bitsets

* Rm comment

* fmt

* Fix lint

* Use variable/constant to provide key

* fmt

* fix lint

* refactor

* Add a prefix for user setting key

* Add license comment

* Add license comment

* Update services/forms/user_form_hidden_comments.go

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* check len == 0

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Gusted <williamzijl7@hotmail.com>
Co-authored-by: 6543 <6543@obermui.de>

options/locale/locale_en-US.ini

@@ -549,6 +549,22 @@ continue = Continue
 cancel = Cancel
 language = Language
 ui = Theme
+hidden_comment_types = Hidden comment types
+comment_type_group_reference = Reference
+comment_type_group_label = Label
+comment_type_group_milestone = Milestone
+comment_type_group_assignee = Assignee
+comment_type_group_title = Title
+comment_type_group_branch = Branch
+comment_type_group_time_tracking = Time Tracking
+comment_type_group_deadline = Deadline
+comment_type_group_dependency = Dependency
+comment_type_group_lock = Lock Status
+comment_type_group_review_request = Review request
+comment_type_group_pull_request_push = Added commits
+comment_type_group_project = Project
+comment_type_group_issue_ref = Issue reference
+saved_successfully = Your settings were saved successfully.
 privacy = Privacy
 keep_activity_private = Hide the activity from the profile page
 keep_activity_private_popup = Makes the activity visible only for you and the admins