Add json_failed_resp_with_message_minimal method

[rousan]

Now the json_failed_resp_with_message method prepends the status code message(Bad Request: ) before the actual message like below:

{
  "status": "failed",
  "code": 400,
  "message": "Bad Request: Username should only contain lowercase alpha-numeric characters"
}

But, it should provide a method not to prepend Bad Request: text e.g. method json_failed_resp_with_message_minimal as below:

{
  "status": "failed",
  "code": 400,
  "message": "Username should only contain lowercase alpha-numeric characters"
}