DOC: improve API reference for prompt_converter module

[paulinek13]

Description

Related: #653

The goal of this PR is to improve the API reference for prompt_converter module (since there are a number of gaps in this list),
and to make sure that the docstrings are formatted properly:

Tests and Documentation

Basically the docs update, no tests modified.

[romanlutz]

Woah you did so many 🔥 nice work

[romanlutz]

I think you'll find that the website generation doesn't like things like

some level of indentation
  - a deeper level of indentation

in the API reference. It's unclear to me why but somehow that doesn't work. At some point in the future I want to switch to JupyterBook2 and MyST instead of all these sphinx extensions like autodoc but as I discovered last night that day is not today (because they don't support API reference generation yet).

[paulinek13]

@romanlutz

I think you'll find that the website generation doesn't like things like

some level of indentation
  - a deeper level of indentation

in the API reference. It's unclear to me why but somehow that doesn't work.

It seems that there must be a new blank line before a list.
As an example:

results in Unexpected indentation error and visually it's not what it should be;

but this is 100% fine: no errors and proper formatting on the page.

[romanlutz]

Great! Then please ignore me and proceed 🤣