feat: Add Config schema docs generator

[fregataa]

resolves #NNN (BA-MMM)

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

[github-advanced-security]

devskim found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

[HyeockJinKim]

For this task to be applied, it is essential to clearly define and proceed with how it will be shown.
Rather than applying the implementation first, please establish a plan for how it will be presented first.