[MM-21919] Add use_channel_mentions permission (#13781)

* MM-21919 Add channel_mention permission

* MM-21919 Fix emojis migration test

* Enforce Channel Mentions on the in the posts api

* MM-21919 Rename permission to use_channel_mentions

Allow posts with channel mentions to still be posted without the permission just don't send notifications to users

* MM-21919 Add tests for a post with @all and @here

* MM-21919 Add use channel mentions to all roles that have create post

* MM-21919 Update app_test to include use_channel_mentions permission in default permissions

model/permission.go

@@ -90,6 +90,7 @@ var PERMISSION_VIEW_MEMBERS *Permission
 var PERMISSION_INVITE_GUEST *Permission
 var PERMISSION_PROMOTE_GUEST *Permission
 var PERMISSION_DEMOTE_TO_GUEST *Permission
+var PERMISSION_USE_CHANNEL_MENTIONS *Permission
 
 // General permission that encompasses all system admin functions
 // in the future this could be broken up to allow access to some
@@ -556,6 +557,13 @@ func initializePermissions() {
 		PERMISSION_SCOPE_SYSTEM,
 	}
 
+	PERMISSION_USE_CHANNEL_MENTIONS = &Permission{
+		"use_channel_mentions",
+		"authentication.permissions.use_channel_mentions.name",
+		"authentication.permissions.use_channel_mentions.description",
+		PERMISSION_SCOPE_CHANNEL,
+	}
+
 	ALL_PERMISSIONS = []*Permission{
 		PERMISSION_INVITE_USER,
 		PERMISSION_ADD_USER_TO_TEAM,
@@ -631,6 +639,7 @@ func initializePermissions() {
 		PERMISSION_INVITE_GUEST,
 		PERMISSION_PROMOTE_GUEST,
 		PERMISSION_DEMOTE_TO_GUEST,
+		PERMISSION_USE_CHANNEL_MENTIONS,
 	}
 }