GN-4937: add support for snippet previews

[elpoelma]

Overview

This (draft) PR updates the editor-plugins to the dev commit found on lblod/ember-rdfa-editor-lblod-plugins#468. It implements collapsible snippet previews.

connected issues and PRs:

GN-4937
lblod/ember-rdfa-editor-lblod-plugins#468

How to test/reproduce

• Start the application
• Create a regulatory statement based on a template containing a snippet placeholder
• Open the 'Insert snippet' modal, and notice that you can preview each of the snippets listed

Checks PR readiness

• UI: works on smaller screen sizes
• UI: feedback for any loading/error states
• Check cancel/go-back flows
• Check database state correct when deleting/updating (especially regarding relationships)
• changelog
• npm lint
• no new deprecations