feat: Raise GoogleAPICallError on REST response errors (#891)

While testing against Showcase, I found that server errors resulted in a large exception stack dump that did not include the body of the erroring response. This PR shortens the stack dump and prints out the request body.

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

@@ -9,8 +9,9 @@ from typing import Callable, Dict, Optional, Sequence, Tuple
 from google.api_core import operations_v1
 {% endif %}
 from google.api_core import gapic_v1       # type: ignore
-from google.auth import credentials as ga_credentials  # type: ignore
-from google.auth.transport.grpc import SslCredentials  # type: ignore
+from google.api_core import exceptions as core_exceptions  # type: ignore
+from google.auth import credentials as ga_credentials      # type: ignore
+from google.auth.transport.grpc import SslCredentials      # type: ignore
 
 import grpc  # type: ignore
 
@@ -214,8 +215,10 @@ class {{ service.name }}RestTransport({{ service.name }}Transport):
             {% endif %}
         )
 
-        # Raise requests.exceptions.HTTPError if the status code is >= 400
-        response.raise_for_status()
+        # In case of error, raise the appropriate core_exceptions.GoogleAPICallError exception
+        # subclass.
+        if response.status_code >= 400:
+            raise core_exceptions.from_http_response(response)
         {% if not method.void %}
 
         # Return the response