👥 Allow to mention groups in the chats when they are a member of the conversation

In group chats I cannot mention a group that is added to this chat.

Todo

• Requires Prepare for group mentions in talk (and comments?) server#29140
• Mention API returns groups which are tracked
• When generating notifications for mentions group members need to be notified
  • Check for conflict with replying
  • Check that the group is a member of the room
• Render group mention suggestion in the input field with icon-group-forced-white + group displayname
• Render group mentions in messages with icon-group-forced-white + group displayname
• Render group mentions primary when the user is a member of the group #9073
• Create issues in iOS and Android to handle those cases
  • Support group mentions talk-android#2860
  • Support group mentions talk-ios#1135
• Allow to prevent @all for non-moderators #9074

[nickvergessen]

Now that we store group memberships that totally makes sense