This is a paired PR along with understrap/postcss-understrap-palette-generator#2
This is a Work In Progress PR.

Description

The idea here is to support theme.json instead of our own custom JSON object that passes bootstrap colors to the gutenberg editor. We're simultaneously updating the postcss plugin along with the theme to test this out.

Motivation and Context

Theme json is taking over for techniques like add_theme_support( 'editor-color-palette', $color_palette ); so we want to support them with Understrap

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [x ] New feature (non-breaking change which adds functionality)
• [ x] Breaking change (fix or feature that would cause existing functionality to change) maybe

Checklist:

• [x ] I pulled my branch from develop.
• [ x] I am submitting my pull request to develop.
• [ x] I have resolved any conflicts merging this pull request would create.
• [x ] I have checked that there aren't other open Pull Requests for the same update/change.
• [x ] My code follows the code style of this project.
• [x ] I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• (Optional) My change requires a change to the documentation.
• (Optional) I have updated the documentation accordingly.
• (Optional) My change requires a change to the translations.
• (Optional) I have updated the translations accordingly.
• composer cs:check has passed locally.
• composer lint:php has passed locally.
• [x ] I have read the CONTRIBUTING document.

Related Issues or Roadmap requests

Related to understrap/postcss-understrap-palette-generator#2