Provide the ability to show the table of contents for API members

[andreyaksenov]

Currently, it's impossible to navigate between API members in docs using the ToC of the right.
For example, it would be convenient to see all msgpack members under the Index ToC entry.
Example from other docs (Docusaurus): https://reactnative.dev/docs/button.

The corresponding feature is added in the 5.2.0 Sphinx version (#6316).
The 5.2.3 adds the capability to disable this feature when required.

How to configure: sphinx-doc/sphinx#6316 (comment)

doc-builder issue: tarantool/doc-builder#22