Make 403 errors due to GCS more verbose.

The current GCS client code neglects to print the nature of a 403 error. For
example, a 403 error can occur because of permissions or rate limiting. The
nature of a 403 error is communicated through the HTTP response. Thus, this
patch extends the 403 error message with the HTTP response returned by curl.

As an example, a 403 error looked like this before this patch:
PermissionDeniedError: Error executing an HTTP request (HTTP response code 403, error code 0, error message '')

With this patch, it might look like:
PermissionDeniedError: Error executing an HTTP request (HTTP response code 403, error code 0, error message ''), response {
 "error": {
  "errors": [
   {
    "domain": "usageLimits",
    "reason": "userRateLimitExceeded",
    "message": "User Rate Limit Exceeded"
   }
  ],
  "code": 403,
  "message": "User Rate Limit Exceeded"
 }
}
PiperOrigin-RevId: 180853399