Docs: adds Docusaurus site

[lukegalbraithrussell]

Summary:

This is the new Docusaurus site. Tested that it builds properly. (You can confirm by looking at the Test Deployment test below.) Is that a bad test name? Writing that sentence makes it seem so.

This is less absurdly large then it looks! ~16,000 of the changed lines are package-lock.json 😬 . 84 of the changed files are the same markdown files re-formatted and moved. (I did a comical amount of git mv so all history is still intact). And I deleted about 30 files.

Folder and file organization

This shares the same structure as the other sites. At large:

docs/
├── content/ (the good stuff. md and mdx files supported)
│   ├── getting-started.md
│   └── concepts
│       └── sending-message.md
├── i18n/ja/ (the japanese translations)
│   ├──docusaurus-theme-classic/ (footer/navbar translations)
│   └──docusaurus-plugin-content-docs/
│       └── current/ (this folder's file names need to exactly match **/content/, but japanese content)
│           ├── getting-started.md
│           └── concepts
│               └── sending-message.md
├── static/
│   ├── css/
│   │   └── custom.css (the css for everything!)
│   └── img/ (the pictures for the site)
│       ├── rory.png 
│       └── oslo.svg 
├── src/
│   ├── pages/ (stuff that isn't docs content. This is empty for this repo)
│   └── theme (only contains the 404 page)
├── docusaurus.config.js (main config file. also where to set navbar/footer)
└── redirects.js (a redirects script because the old site used # as pages which docusaurus can't handle)
└── sidebar.js (manually set where the content docs are in the sidebar.)

The default name for my content folder was docs but docs/docs was silly. I am open to other names though.

Docs pages: slugs and links

The organization of pages is purposefully kept as similar to the current layout of pages so developers don't get jarred from both a site change and page changes. Slugs are all named matching that previous organization - i.e. something in the basics or the advanced folder (and others) has the concepts slug: /bolt-js/concepts/authorization. This is slightly different than the previous site, which took the form of /bolt-js/concepts#authorization. They're all separate pages, not headers now. I've written a script to redirect the old concepts#topic to the proper concepts/topic. Any previous working link will properly redirect.

All .md files were renamed (yes, I used git mv) to match the title and the slug. Everything now matches up.

All markdown reference links were also updated to be up-to-date and working. If it's a link on the site, it now works. I also stripped all the pages of any residual HTML or custom formatting. They should all be the most basic of markdown now.

Editing and managing the site

The README contains a basic docs editing guide. You don't need to worry about the site unless you're touching something inside the /docs folder.

There is a new action workflows: it does a test build on docs PRs and deploys the site on merges to main.

Next steps

This wouldn't be a DevRel project without some fast follows. This is what I plan on doing after all the sites are live:

• Set up action workflow to update this custom.css if the main site's custom.css is changed.
• Sanitize the GitHub releases notes so the generated changelog can work fully automatically. For now, I'll add it in myself during releases.
• I recognized some copy directly taken from the API site (about modals, app home, etc). I remember that copy because I deleted all of it on our site and rewrote it lol. Will do the same here. (It'll remove length, promise!)
• General copy editing (I avoided this the best I could in this PR).
• Update tutorials with self-updating GitHub code snippet links.
• Write a little introduction. Right now, / just redirects to /getting-started since that's all this site had.

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.07%. Comparing base (59923f5) to head (29b9b99).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2174   +/-   ##
=======================================
  Coverage   82.07%   82.07%           
=======================================
  Files          18       18           
  Lines        1545     1545           
  Branches      443      443           
=======================================
  Hits         1268     1268           
  Misses        179      179           
  Partials       98       98           

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[filmaj]

LGTM! Left a few notes/questions but overall looks great!