feat: add POST and DELETE endpoints for objects

[sarthakgupta072]

Description

• add specs for POST /objects and DELETE /objects/{object_id} endpoints
• implement endpoint logic
• properties id, self_uri and access_id in the Object definition of the DRS specs are auto-populated upon POSTing objects

Fixes #8 and #10

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)
• [x] Documentation update

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] I have not reduced the existing code coverage
• [x] I have added docstrings following the Python style guidelines of this project to all new modules, classes, methods and functions are documented with docstrings following; I have updated any previously existing docstrings, if applicable
• [x] I have updated any sections of the app's documentation that are affected by the proposed changes, if applicable