[WIP] New reference documentation

[jenningsanderson]

Moving to Pydantic!

This PR updates and simplifies the docs to show easier, table-based schema docs.

Enhancements to docs code:

1. Removes Docusaurus JSON Schema Plugin.
2. Enables (significantly) faster builds.
3. Reduction in serving of raw YAML files.

/schema/reference Updates:

Today, everything available under docs.overturemaps.org/schema lives here: https://github.com/OvertureMaps/schema/tree/dev/docs/schema. When docusaurus builds the docs, it fetches the .mdx, schema, and examples from the schema repo. This is a lot of moving parts and kind of ugly.

This PR removes that requirement in favor of simple, machine-readable markdown files that can be self-generated by the schema and used by documentation.

See https://staging.overturemaps.org/docs/pr/222/schema/reference/address/ for an example of how we envision these reference docs rendering.

Next Steps:

Before this is ready to merge, we need to develop the ability for the schema to create self-describing documentation with examples as markdown files, example:

# Place

A Place is a point representation of a real-world facility, service, or amenity.

Place features are compatible with GeoJSON Point features.

## Fields

| Name | Type | Description |
|-----:|:----:|-------------|
| `id` | `string` |  |
| `theme` | `"places"` |  |
| `type` | `"place"` |  |
| `geometry` | `geometry` | Position of the place |
| `names` | `object` (`[Names](../../Names/names)`) (optional) |  |
| `names.primary` | `string` | The most commonly used name. |
| `names.common` | `object` (optional) |  |
...

## Examples

| Column | Value |
|-------:|-------|
| `geometry` | `POINT (-151.7990018 -79.5664328)` |
| `categories.alternate` | `null` |
| `categories.primary` | `media_news_website` |
| `confidence` | `0.8015267175572519` |
| `websites` | `[https://www.primenewsmonde.bj/]` |

The full schema should be a series of markdown files nested by theme/type that have relative links. We can adjust the SmartTable component as necessary to make the links work — but the markdown should be a nice, standalone set of files.

If the examples that were embedded were actually derived from the examples in the schema repository after being validated by the schema itself, that would be best case scenario.

Once this ability exists, we can update this repository to fetch these markdown files (or checkout schema and build the markdown as part of the publish). The idea is these files can be dropped directly into docs/schema to power this part of the documentation.

Docs Preview

Example: