fix: add gcloud-python header to user agent (#9551)

* fix: add gcloud-python header to user agent

Author: crwilcox

storage/google/cloud/storage/_http.py

@@ -36,6 +36,11 @@ def __init__(self, client, client_info=None, api_endpoint=DEFAULT_API_ENDPOINT):
         self.API_BASE_URL = api_endpoint
         self._client_info.client_library_version = __version__
 
+        # TODO: When metrics all use gccl, this should be removed #9552
+        if self._client_info.user_agent is None:  # pragma: no branch
+            self._client_info.user_agent = ""
+        self._client_info.user_agent += " gcloud-python/{} ".format(__version__)
+
     API_VERSION = "v1"
     """The version of the API, used in building the API call's URL."""