Deploy docs from this repo, deprecate spectacle-docs

[kale-stew]

Description

We should sync the docs that exist within this repo with whatever is in spectacle-docs, and then set up a config (maybe deployed through CI when docs are changed?) to serve those docs to the docs hosted on the Formidable website from this repo directly.

Proposal

• Move docs over to this repo, make sure they're up to date with v5.x.x (current Spectacle)
• Add Gatsby config to serve/style the docs correctly
• Add a deployment step to CI, trigger on /docs changes

If we do the above before rolling out our v6 release, it should be easier to pin the last release of Classic Spectacle to the correct documentation.