PRO-8316: move docs to /docs, mechanism to deploy

[boutell]

To test this:

• Be sure to npm install, I added deps in this branch
• Test locally as usual
• brew install muffet to find broken links
• Try out the new npm run find-broken-links script, note it will find a lot of 403's and a few 404's on sites that just don't allow utilities like muffet, but it's generally very useful. I fixed a lot of 404's, but I left a bunch of links that do not 404 but have bad anchors because that wasn't my primary goal, see: pro-8581 for a list
• Try npm run deploy-staging, which requires you have a checkout of apostrophecms-website at ~/apostrophecms/apostrophecms-website. Note that it will update our develop branch and push it
• Evaluate staging itself

[linear]

PRO-8316 Host documentation as a subdirectory to optimize all of the great Docs content we've invested in.