added docstrings for api_audience and interceptor

Author: daniel-sanche

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

@@ -103,6 +103,10 @@ class {{ service.name }}Transport(abc.ABC):
                 your own client library.
             always_use_jwt_access (Optional[bool]): Whether self signed JWT should
                 be used for service account credentials.
+            api_audience Optional[str]: The intended audience for the API calls
+                to the service that will be set when using certain 3rd party
+                authentication flows. Audience is typically a resource identifier.
+                If not set, the host value will be used as a default.
         """
         {% if service.any_extended_operations_methods %}
         self._extended_operations_services: Dict[str, Any] = {}

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

@@ -169,6 +169,10 @@ class {{ service.name }}GrpcTransport({{ service.name }}Transport):
                 your own client library.
             always_use_jwt_access (Optional[bool]): Whether self signed JWT should
                 be used for service account credentials.
+            api_audience Optional[str]: The intended audience for the API calls
+                to the service that will be set when using certain 3rd party
+                authentication flows. Audience is typically a resource identifier.
+                If not set, the host value will be used as a default.
 
         Raises:
           google.auth.exceptions.MutualTLSChannelError: If mutual TLS transport

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

@@ -218,6 +218,10 @@ class {{ service.grpc_asyncio_transport_name }}({{ service.name }}Transport):
                 your own client library.
             always_use_jwt_access (Optional[bool]): Whether self signed JWT should
                 be used for service account credentials.
+            api_audience Optional[str]: The intended audience for the API calls
+                to the service that will be set when using certain 3rd party
+                authentication flows. Audience is typically a resource identifier.
+                If not set, the host value will be used as a default.
 
         Raises:
             google.auth.exceptions.MutualTlsChannelError: If mutual TLS transport

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

@@ -135,6 +135,12 @@ class {{service.name}}RestTransport(_Base{{ service.name }}RestTransport):
             url_scheme: the protocol scheme for the API endpoint.  Normally
                 "https", but for testing or local servers,
                 "http" can be specified.
+            interceptor Optional[{{ service.name }}RestInterceptor]:  Interceptor used
+                to manipulate requests, request metadata, and responses.
+            api_audience Optional[str]: The intended audience for the API calls
+                to the service that will be set when using certain 3rd party
+                authentication flows. Audience is typically a resource identifier.
+                If not set, the host value will be used as a default.
         """
         # Run the base constructor
         # TODO(yon-mg): resolve other ctor params i.e. scopes, quota, etc.

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

@@ -134,6 +134,8 @@ class Async{{service.name}}RestTransport(_Base{{ service.name }}RestTransport):
             url_scheme (str): the protocol scheme for the API endpoint.  Normally
                 "https", but for testing or local servers,
                 "http" can be specified.
+            interceptor Optional[{{ service.name }}RestInterceptor]:  Interceptor used
+                to manipulate requests, request metadata, and responses.
         """
         # Run the base constructor
         super().__init__(