add errata_id param to ContentViewFilterRule

errata param already excists but the Satellite expects errata_id to be set to the Red Hat Errata ID when creating Content View Filter Rules, if I use the errata field Nailgun ends up sending the Database ID to Satellite, but i need to Red Hat Errata ID.

nailgun/entities.py

@@ -1865,6 +1865,7 @@ def __init__(self, server_config=None, **kwargs):
             ),
             'end_date': entity_fields.DateField(),
             'errata': entity_fields.OneToOneField(Errata),
+            'errata_id': entity_fields.StringField(),
             'max_version': entity_fields.StringField(),
             'min_version': entity_fields.StringField(),
             'name': entity_fields.StringField(