Introduce a blueprint for WordPress preview

[EvanHerman]

Description

Introduce a blueprint.json file that is a template for a live preview on WordPress.org.

• Same file as the one currently on WordPress.org, so when this PR is merged it won't overwrite the existing one.
  • https://plugins.svn.wordpress.org/coblocks/assets/blueprints/
• The live preview is currently only visible to logged in plugin committers. It can be enabled publicly from the WordPress.org plugin page advanced tab.

Thoughts

We can import a .wxz file. Maybe we setup a number of CoBlocks blocks so that when the page loads there are a number of blocks on the page already?

Screenshots

Types of changes

New feature (non-breaking change which adds functionality)

How has this been tested?

Test Preview link on the WordPress.org plugin page.

Acceptance criteria

• Add a blueprint.json file so users can test out CoBlocks before installing it.

Checklist:

• [x] My code is tested
• [x] I've added proper labels to this pull request