WIP - feat: Add Docusaurus rewrite of docs site

[yhakbar]

Description

So far, this is just a bare minimum Docusaurus server so that we can start prototyping.

We'll also be exploring Starlight, as it's another common documentation tool.

The end goal of this experimentation is to have another docs site hosted concurrently with the existing Jekyl based one that users can opt-in to. After the new docs site is live for a while, and users are happy with it, we'll swap out the default so that users navigate to the rewrite by default.

TODOs

Read the Gruntwork contribution guidelines.

• Update the docs.
• Run the relevant tests successfully, including pre-commit checks.
• Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.
• Include release notes. If this PR is backward incompatible, include a migration guide.

Release Notes (draft)

Added / Removed / Updated [X].

Migration Guide