New documentation site (Docusaurus) (#398)

Solves #323, related to #217.

# Description

This commit revisits the documentation site. Here's a preview:

https://wordpress.github.io/wordpress-playground/docs/blueprints-api/steps/

(I went ahead and deployed it to github.io even tough this PR isn't
merged yet since it's a much better entry point to the project).

## What changed?

This PR:

* Adds the missing bits of the documentation and improve the structure
* Adds the first interactive examples with more to come
* Generates parts of the docs directly from the doc strings
* Adds link validation
* Improves readability and interconnectedness between the content pages
and the API reference

It is the first step towards addressing the following issues with the
current documentation:

* It is incomplete
* It is not interactive
* It is not connected to code and a PR can make it go stale
* It is not testable and there's no way to know whether the code
snippets still work
* API docs can be hard to read
* Dead links – no link validation

## Technical details

* Docusaurus uses [MDX](https://mdxjs.com/) which is essentially
Markdown + React.
* TypeScript documentation is generated with Typedoc and included using
a Docusaurus plugin.
* Repeatable code snippets are abstracted to fragments. Updating them
once updates all the occurrences in the docs.
* We can use React components inside the mdx files. Super useful for
code examples and auto-displaying information derived from the
TypeScript code.

A few practical example of what's so good about this approach

### API Reference integration

<img width="600" alt="CleanShot 2023-05-21 at 14 07 17@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/9a755d3c-e205-4b75-b3c4-bb0cd2bcd131">

### Runnable code examples

<img width="530" alt="CleanShot 2023-05-21 at 14 03 57@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/466bb639-1bda-4303-9ce6-6a05eb234cab">
<img width="530" alt="CleanShot 2023-05-21 at 14 03 50@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/c74916b3-0890-437e-beab-87b60b480fab">

### Reusable content

<img width="400" alt="CleanShot 2023-05-21 at 14 06 38@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/78b3b7b1-042d-46c7-bfa4-c87f2f115d2e">
<img width="400" alt="CleanShot 2023-05-21 at 14 06 14@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/b15d3238-5bca-47e1-bc2e-7ff31a58acc7">

### Inline TOC

<img width="300" alt="CleanShot 2023-05-21 at 14 05 14@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/42a10f13-4f54-4a2c-bb5a-d9a66db85333">
<img width="300" alt="CleanShot 2023-05-21 at 14 05 35@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/e5e374c7-d790-4c89-beb0-f064ccb8588c">

### Deriving Blueprint steps from code

With this PR, adding a Blueprint step into the codebase will
automatically add it to the docs. If it has a usage example, it will be
rendered as a live code snippet. In the future, it will be editable and
the CI will verify whether it still works.

<img width="441" alt="CleanShot 2023-05-21 at 01 23 22@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/80b265f9-6954-45a1-bd35-e888fe3e5f91">

### Docusaurus prevents broken links

<img width="450" alt="CleanShot 2023-05-21 at 00 58 36@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/b5e57360-9f2d-4676-9888-557c4c0bcf0c">

### TypeScript comment embedded inside of a documentation page

<img width="343" alt="CleanShot 2023-05-21 at 01 41 58@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/c4cf1811-549e-4d21-ae8a-3009f8024b5a">

<img width="445" alt="CleanShot 2023-05-21 at 01 42 24@2x"
src="https://github.com/WordPress/wordpress-playground/assets/205419/5d6a9d5b-1286-466b-a082-fcdcc5659439">

.github/workflows/ci.yml

@@ -12,6 +12,7 @@ jobs:
             - uses: actions/checkout@v2
               with:
                   fetch-depth: 0
+            - uses: actions/setup-node@v3
             - uses: nrwl/nx-set-shas@v3
               with:
                   main-branch-name: 'trunk'

.gitignore

@@ -8,6 +8,8 @@ var
 .vitepress
 __pycache__
 packages/php-wasm/node/src/test/__test*
+packages/docs/site/src/model.json
+.docusaurus
 dist.zip
 
 # dependencies

.vscode/settings.json

@@ -16,5 +16,12 @@
 	},
 	"autoImportFileExcludePatterns": [
 		"@wp-playground/client"
-	]
+	],
+	"frontMatter.content.pageFolders": [
+		{
+			"title": "Start here",
+			"path": "[[workspace]]/packages/docs/site/docs/01-start-here"
+		}
+	],
+	"git.ignoreLimitWarning": true
 }

CODE_OF_CONDUCT.md

@@ -0,0 +1,11 @@
+This project comes under the WordPress [Etiquette](https://wordpress.org/about/etiquette/):
+
+In the WordPress open source project, we realize that our biggest asset is the community that we foster. The project, as a whole, follows these basic philosophical principles from The Cathedral and The Bazaar.
+
+-   Contributions to the WordPress open source project are for the benefit of the WordPress community as a whole, not specific businesses or individuals. All actions taken as a contributor should be made with the best interests of the community in mind.
+-   Participation in the WordPress open source project is open to all who wish to join, regardless of ability, skill, financial status, or any other criteria.
+-   The WordPress open source project is a volunteer-run community. Even in cases where contributors are sponsored by companies, that time is donated for the benefit of the entire open source community.
+-   Any member of the community can donate their time and contribute to the project in any form including design, code, documentation, community building, etc. For more information, go to make.wordpress.org.
+-   The WordPress open source community cares about diversity. We strive to maintain a welcoming environment where everyone can feel included, by keeping communication free of discrimination, incitement to violence, promotion of hate, and unwelcoming behavior.
+
+The team involved will block any user who causes any breach in this.