Set up Docusaurus init, CI, GH Pages

See how FxA Ecosystem Platform is set up (publish-gh-pages script): https://github.com/mozilla/ecosystem-platform Also see GH pages site publishing: https://docs.github.com/en/github/working-with-github-pages/configuring-a-publishing-source-for-your-github-pages-site Also see Docusarus' publishing docs: https://docusaurus.io/docs/en/publishing

It would be nice if we could have some sort of doc-hub (perhaps docs/ is okay, but we already have app/experimenter/docs) root-level directory in Experimenter to house Docusaurus and related docs to keep everything in main. We don't want all of Experimenter's CI jobs to run in this directory or branch, but just a task for CI to push the build out to the gh-pages branch.

If this proves to be impossible or particularly tricky, we can also create a separate branch and tell GH Pages to deploy from there (and exclude the branch from Experimenter typical CI runs). However, if this needs to be done, we'll also need to file another ticket to set up Dependabot for this branch since it'll remain separate from main.

Also, update the experimenter front-page README with a note about the doc hub and GH Pages link.

┆Issue is synchronized with this Jira Task ┆Issue Number: EXP-1023

mozilla / experimenter

Set up Docusaurus init, CI, GH Pages #4718