MM-14675: Eliminates implicit GroupChannel/GroupTeam associations. (#13199)

* MM-14675: Upserts GroupTeam when GroupChannel is linked.
MM-14675: Delete all associated GroupChannels when deleting a GroupTeam.
MM-14675: Using replica DB where possible.
MM-14675: Updates create method used in tests.

* MM-14675: Removes unnecessary DB retrieval of GroupSyncable record.

api4/channel_test.go

@@ -2269,7 +2269,7 @@ func TestAddChannelMember(t *testing.T) {
 	CheckErrorMessage(t, resp, "api.channel.add_members.user_denied")
 
 	// Associate group to team
-	_, appErr = th.App.CreateGroupSyncable(&model.GroupSyncable{
+	_, appErr = th.App.UpsertGroupSyncable(&model.GroupSyncable{
 		GroupId:    th.Group.Id,
 		SyncableId: privateChannel.Id,
 		Type:       model.GroupSyncableTypeChannel,