feat: Encode numeric enums parameter with REST requests (#1399)

This adds `$alt=json;enum-encoding=int` to the query string if numeric enums are enabled for REST transport.

Author: vchudnov-g

gapic/ads-templates/%namespace/%name/%version/%sub/services/%service/transports/rest.py.j2

@@ -341,6 +341,10 @@ class {{service.name}}RestTransport({{service.name}}Transport):
             query_params.update(self._get_unset_required_fields(query_params))
             {% endif %}{# required fields #}
 
+            {% if opts.rest_numeric_enums %}
+            query_params["$alt"] = "json;enum-encoding=int"
+            {% endif %}
+
             # Send the request
             headers = dict(metadata)
             headers['Content-Type'] = 'application/json'

gapic/templates/%namespace/%name_%version/%sub/services/%service/transports/rest.py.j2

@@ -349,6 +349,10 @@ class {{service.name}}RestTransport({{service.name}}Transport):
             query_params.update(self._get_unset_required_fields(query_params))
             {% endif %}{# required fields #}
 
+            {% if opts.rest_numeric_enums %}
+            query_params["$alt"] = "json;enum-encoding=int"
+            {% endif %}
+
             # Send the request
             headers = dict(metadata)
             headers['Content-Type'] = 'application/json'