feat: add status_code property on http error handling (#1185)

Fixes #1183 🦕
Fixes #1255 🦕
- Add status code property in http error handler class.
- Resolve issue where error_details is not populated.
diff --git a/docs/start.md b/docs/start.md
index def0c4a..9207620 100644
--- a/docs/start.md
+++ b/docs/start.md
@@ -99,7 +99,7 @@
 try:
     response = request.execute()
 except HttpError as e:
-    print('Error response status code : {0}, reason : {1}'.format(e.resp.status, e.error_details))
+    print('Error response status code : {0}, reason : {1}'.format(e.status_code, e.error_details))
 ```
 
 Alternatively, you can combine previous steps on a single line: