DEV: Buff theme install rake task - more options (PR #9394)

Add option to install a theme component to all installed themes.

Also add ability to pass a JSON string into rake themes:install

bin/rake themes:install -- '--{"placeholder": {"url": "https://github.com/discourse/discourse-placeholder-theme-component.git", "install_to_all_themes": true}}'

GitHub

The title of this pull request changed from “Allow JSON string to be passed to theme install rake task” to "DEV: Buff theme install rake task - more options

Not ready for review.

Cool, seems like a nice improvement to me!