3145 add openapi specification for /tables/ endpoint

[varshadr]

Fixes #3145

This PR adds OpenAPI Specification for the /tables/ endpoint to the codebase

Technical details

• Refined custom_preprocessing_hook to include '/api/db/v0/tables/' endpoint.
• Finally, generated the spec for /tables/ endpoint using the _./manage.py spectacular --color --file schema.yml_ command

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• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[varshadr]

@silentninja, could you please review the spec I generated for /tables/ endpoint?