Feat: create custom blocks

[rise-erpelding]

Description

• Adds example plugins
• Allows for multiple blocks to be added without additional configuration in example-blocks/package.json or example-blocks/example-blocks.php

Closes #22

To Validate

1. Make sure all PR Checks have passed
2. Pull down this branch
3. Run npm run plugins:install
4. Run npm start
5. Go to http://localhost:8000/wp-admin/plugins.php and activate the "Example Blocks" plugin.
6. Go to posts, create a new post or edit an existing post, and confirm that the "Reverse String" and "Hello World" blocks are available blocks (under its own section, "Example Custom Blocks").
7. Preview the post and confirm that blocks are displayed as expected.
8. Run added lint scripts (npm run lint:plugins:js, npm run lint:plugins:css, npm run plugins:format) and confirm that they appear to be working.

[dustin-jw]

Overall this works great! I just had a few nitpicks and npm script things that could be adjusted a bit.