feat: Generate API docs

[masci]

Add a hatch command hatch run docs to run pydoc-markdown and generate the markdown file containing the API docs for the integration.

[vblagoje]

When I run this branch I get:

(haystack) ➜  chroma git:(massi/chroma-pydoc) ✗ hatch run docs
cmd [1] | pydoc-markdown pydoc/document_stores.yml
/Users/vblagoje/Library/Application Support/hatch/env/virtual/chroma-haystack/bdNP9TFm/chroma-haystack/lib/python3.10/site-packages/haystack_pydoc_tools/renderers.py:60: UserWarning: README_API_KEY env var is not set, using a placeholder category ID
  self.categories = self._readme_categories(self.version)

I suppose the key README_API_KEY is required. LMK if I can be of any help here 😄