Enhance Ghost comment mitigation Settings (#14392)

* refactor models.DeleteComment and delete related reactions too

* use deleteComment for UserDeleteWithCommentsMaxDays in DeleteUser

* nits

* Use time.Duration as other time settings have

* docs

* Resolve Fixme & fix potential deadlock

* Disabled by Default

* Update Config Value Description

* switch args

* Update models/issue_comment.go

Co-authored-by: zeripath <art27@cantab.net>

Co-authored-by: zeripath <art27@cantab.net>

models/issue_assignees.go

@@ -82,7 +82,7 @@ func isUserAssignedToIssue(e Engine, issue *Issue, user *User) (isAssigned bool,
 }
 
 // ClearAssigneeByUserID deletes all assignments of an user
-func clearAssigneeByUserID(sess *xorm.Session, userID int64) (err error) {
+func clearAssigneeByUserID(sess Engine, userID int64) (err error) {
 	_, err = sess.Delete(&IssueAssignees{AssigneeID: userID})
 	return
 }