Replace pydoc-markdown with a maintained documentation tool

[alperenkose]

Is your feature request related to a problem?

pydoc-markdown is not maintained for more than a year and it fails to run if databind dependency is updated to '>=4.5' with the below error. This also prevents other dependencies like typing-extensions to be updated.

❯ make documentation                                                                                                                                                       ─╯
pydoc-markdown
Traceback (most recent call last):
  File "/Users/akose/Development/paloalto/pan-os-upgrade-assurance/.venv/bin/pydoc-markdown", line 5, in <module>
    from pydoc_markdown.main import cli
  File "/Users/akose/Development/paloalto/pan-os-upgrade-assurance/.venv/lib/python3.8/site-packages/pydoc_markdown/__init__.py", line 34, in <module>
    import databind.json
ModuleNotFoundError: No module named 'databind.json'
make: *** [documentation] Error 1

Typing extensions dependency of databind=4.4.2 preventing typing-extensions to be updated:

Because databind-core (4.4.2) depends on typing-extensions (>=3.10.0,<4.7)
 and panos-upgrade-assurance depends on typing-extensions (>=4.12.2), databind-core is forbidden.
So, because panos-upgrade-assurance depends on databind-core (4.4.2), version solving failed.

Describe alternatives you've considered

We might consider mkdocstrings or research other altenatives which would require minimal change in the docstrings.

Additional context

We need to carefully select the tool as the change might result in a significant change in the format of docstrings.