Add API Documentation

[keshav-space]

Use drf-spectacular for swagger flavour API Documentation.

Why use drf-spectacular over DRF's Built-in Documentation?

• Built-in Documentation depends on CoreAPI and starting v3.10 DRF began deprecating CoreAPI in favor of OpenAPI [Ref]
• Starting v3.14 DRF began deprecating Built-in support for OpenAPI schema in favor of 3rd party packages like drf-spectacular [Ref]
• fixes Create API documentation #225

Screenshots

[pombredanne]

@keshav-space we should merge this soon enough! do you mind rebasing?

[pombredanne]

Also would have a screenshot that shows up how to use it? And/or some simple instructions and a Changelog entry?

[JonoYang]

@keshav-space Thanks!