Implement Markdown reference renderer

[seesharprun]

This pull request refactors the entire documentation system to use Markdown files with these major changes:

• All documentation is pulled from the documentdb/docs repository
• Reference documentation is pulled from Markdown with YAML front matter metadata instead of YAML files directly. This PR also updates the codebase to support this new format.
• Articles are pulled from Markdown with YAML files for navigation
• Article metadata is pulled from YAML front matter or partial files
• This update also includes a rework of the navigation menu for reference content to closer match the expected structure of reference documentation.

You can review a sample build of the Next.js site in my fork here:

• https://seesharprun-documentdb-prototype.github.io/docs/reference

  

Test locally

1. Clone this code

2. Get dependencies with npm install

3. Run site

   • Debug with npm run dev

   • Statically build and host the site using npm run build and npm run start

4. Check all new documentation

   • http://localhost:3000/docs/getting-started

   • http://localhost:3000/docs/postgres-api

   • http://localhost:3000/docs/documentdb-local

   • http://localhost:3000/docs/architecture

   • http://localhost:3000/docs/reference

   • http://localhost:3000/docs/reference/commands

   • http://localhost:3000/docs/reference/commands/aggregation

   • http://localhost:3000/docs/reference/commands/aggregation/count

   • http://localhost:3000/docs/reference/operators

   • http://localhost:3000/docs/reference/operators/evaluation-query

   • http://localhost:3000/docs/reference/operators/evaluation-query/$regex

[seesharprun]

This PR will need to be reworked as the content now comes from https://github.com/documentdb/docs.

I'll mark as ready again once the PR has been updated.

[seesharprun]

@abinav2307, this is the pull request to pull documentation from documentdb/docs and render it on your site.