Group serializer special v1 functionality

Returns a related `inventory_source` and related link for groups
if accessed from /api/v1/, but not for API v2.
Also inserts corresponding fields to inventory source serializer.
Keep migrated manual sources and auto-create in API v1.

awx/main/migrations/0037_v320_release.py

@@ -28,7 +28,7 @@ class Migration(migrations.Migration):
         migrations.AlterField(
             model_name='inventorysource',
             name='deprecated_group',
-            field=models.ForeignKey(related_name='deprecated_inventory_source', default=None, null=True, to='main.Group'),
+            field=models.OneToOneField(related_name='deprecated_inventory_source', null=True, default=None, to='main.Group'),
         ),
         migrations.AlterField(
             model_name='inventorysource',

awx/main/migrations/0038_v320_data_migrations.py

@@ -19,7 +19,6 @@ class Migration(migrations.Migration):
     operations = [
         # Inventory Refresh
         migrations.RunPython(migration_utils.set_current_apps_for_migrations),
-        migrations.RunPython(invsrc.remove_manual_inventory_sources),
         migrations.RunPython(invsrc.remove_inventory_source_with_no_inventory_link),
         migrations.RunPython(invsrc.rename_inventory_sources),
     ]

awx/main/migrations/_inventory_source.py

@@ -10,6 +10,7 @@ def remove_manual_inventory_sources(apps, schema_editor):
     Group creation and we would use the parent Group as our interface for the user.
     During that process we would create InventorySource that had a source of "manual".
     '''
+    # TODO: use this in the 3.3 data migrations
     InventorySource = apps.get_model('main', 'InventorySource')
     # see models/inventory.py SOURCE_CHOICES - ('', _('Manual'))
     logger.debug("Removing all Manual InventorySource from database.")