Start consolidation of documentation

[PGijsbers]

Change

Expand on the documentation, and start consolidating it into one place.
The current state is not yet ready for public consumption, but I think the idea is clear and ready for feedback.

While I would not require it to be perfect, I do think we need a little extra effort to modify existing documentation to better make use of the new structure. The follow up would be to do improve that integration and set up an automatic build and deploy workflow.

How to Test

Locally:

python -m pip install mkdocs-material
python -m mkdocs serve

Visit http://localhost:8000/docs (assuming you do not have the metadata catalogue service running locally).
You can browse the documentation.

Since these are documentation changes, they do not warrant additional tests.
In fact, I disabled unit tests from the pre-commit hook if only markdown files are changed in a commit.

Checklist

• Tests have been added or updated to reflect the changes, or their absence is explicitly explained.
• Documentation has been added or updated to reflect the changes, or their absence is explicitly explained.
• A self-review has been conducted checking:
  • No unintended changes have been committed.
  • The changes in isolation seem reasonable.
  • Anything that may be odd or unintuitive is provided with a GitHub comment explaining it (but consider if this should not be a code comment or in the documentation instead).
• All CI checks pass before pinging a reviewer, or provide an explanation if they do not.

Related Issues

N/A

[Taniya-Das]

Looks good to me.