Change custom type field to default one

With the new Elasticsearch does not support custom field type [1].

[1] https://www.elastic.co/guide/en/elasticsearch/reference/7.17/removal-of-types.html#_custom_type_field

Change-Id: I0b154da0a4736c6b7758f9936356d5b7097c35ad

zuul/driver/elasticsearch/connection.py

@@ -95,7 +95,7 @@ class ElasticsearchConnection(BaseConnection):
     def setIndex(self, index):
         settings = {
             'mappings': {
-                'zuul': {
+                '_doc': {
                     "properties": self.properties
                 }
             }