[docs] Refine docs site

Fixes #68

Changelog

Move data model tables to the front page, moving the list of terms to the second tab
Allow long tables to be scrollable (current max height set to 650px)
Replace previous "Vocab" pages with "Valid Values" pages, so that all valid value tables for a given model are displayed on the same page (whereas before, terms were split by category)
- Add a sub-page that will display all valid value terms (using all_valid_values.csv as the source)
Add Attribute: to the headers on the valid values pages
Replace Attribute with Valid Values in the valid values tables
Add Validation Rules to the data model tables, displaying None for any attributes with no rules
Add a hooks script to pre-process the model template files (modules/**/annotationProperty.csv) so that:
- Attributes with a list of valid values are linked to the valid values table
- Only columns only relevant to the end-user are used
- Use "DM Sans" - Sage's latest official font/typeface

Install mkdocs, mkdocs-material, mkdocs-table-reader-plugin, pandas, ideally in a virtual environment, e.g.

conda create -n docs python=3.12
conda activate docs
pip install mkdocs mkdocs-material mkdocs-table-reader-plugin pandas

Change directories to the repo and checkout this branch:
```
cd path/to/data-models 
git checkout docs-68
```
Start the server:
```
mkdocs serve
```
This will serve the documentation on http://127.0.0.1:8000.

Once done, stop the server with Ctrl + C