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/group_test.go

@@ -645,7 +645,7 @@ func TestGetGroupsByChannel(t *testing.T) {
 	})
 	assert.Nil(t, err)
 
-	_, err = th.App.CreateGroupSyncable(&model.GroupSyncable{
+	_, err = th.App.UpsertGroupSyncable(&model.GroupSyncable{
 		AutoAdd:    true,
 		SyncableId: th.BasicChannel.Id,
 		Type:       model.GroupSyncableTypeChannel,
@@ -698,7 +698,7 @@ func TestGetGroupsByTeam(t *testing.T) {
 	})
 	assert.Nil(t, err)
 
-	_, err = th.App.CreateGroupSyncable(&model.GroupSyncable{
+	_, err = th.App.UpsertGroupSyncable(&model.GroupSyncable{
 		AutoAdd:    true,
 		SyncableId: th.BasicTeam.Id,
 		Type:       model.GroupSyncableTypeTeam,