Add messages to Empty responses & Empty List Responses

[sumit-badsara]

Describe the bug
For most of the 201_CREATED responses are empty.
We need to respond with atleast a success message that the resource has been created successfully.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'http://localhost:8000/api/users/register/'
2. Register a new user
3. See Response

Expected behavior
Return a relevant dictionary to response
Example for above specified endpoint :

{
   "detail":"User has been registered successfully"
}

[naveennvrgup]

Also for some list API endpoints, when list is empty, return a response rather than an empty list.

1. @BadduCoder I have removed this line from the issue description as an empty list is more preferred than a response in the frontend (for this case).
2. This is because if the response detail is provided we have to check for whether it is array or object etc., Just adding more point of failure.
3. If the array is empty we will provide an appropriate message in the frontend only. 😇

[sumit-badsara]

Okay! let's then roll then 🔥