Add robots.txt to disable Search Engine indexing

[TomFern]

What

Enable noIndex in the docusaurus config to prevent indexing search engines

Why

We don't want any search indexes to access the in-progress pages. We'll re-enable indexing when the site is in production.

Addresses #88

Checklist:

Use a checklist to confirm:

• The branch is up-to-date with the main branch.
• Update follows the docs style guide.
• Changes have been tested locally.