feat: custom block generators

[dustin-jw]

Description

This work replaces the example blocks plugin with generators for scaffolding new custom blocks plugins and individual custom blocks. This further reduces the amount of boilerplate that a developer would need to delete (or forget is still there) when starting a new project.

Closes #113

To Validate

1. Make sure all PR Checks have passed
2. Pull down this branch
3. Run npm ci (there's a new dependency for one of the generators)
4. Run npm start
5. Confirm that the WordPress Plugins admin page no longer lists the "Example Blocks" plugin (existing posts that used the blocks may warn you about the blocks being unsupported, but you can convert them to HTML)
6. Run npm run generate:custom-blocks-plugin and answer the prompts to create a test plugin
7. Run npm run generate:custom-block and answer the prompts to create a test block within the test plugin
8. Confirm that all the files you would expect for a custom block are created in src/plugins (compare to main as an example)
9. Confirm that two new npm scripts are added to package.json
10. Confirm that a new volume mapping is added to docker-compose.yml
11. Restart your development process (Ctrl+C, then npm start) to pick up the package.json and docker-compose.yml changes
12. Go to the WordPress Plugins admin page and confirm that your test plugin is available and can be activated
13. Activate the plugin
14. Add or edit a post and add your test block, confirming that it works as expected both in the editor and on the site when viewing the page

[rise-erpelding]

Working as expected!! Nice job!