GN-5055: adjust data-model for connected snippet lists

[elpoelma]

Overview

This PR slightly adjusts the data-model for connected snippet lists:

• Rename snippet-lists JSON:API relationship defined on document-container to linked-snippet-lists for clarity
• Add linked-snippet-lists JSON:API relationship to snippet data-model
• Remove unused templates JSON:API relationship of snippet-list data-model

This PR also adds a migration which renames the ext:hasSnippetLists predicate to ext:linkedSnippetList for clarity.

connected issues and PRs:

GN-5055
lblod/frontend-reglementaire-bijlage#299

How to test/reproduce

• Ensure the migration has run successfully
• The /snippets and /document-containers JSON:API routes should now also provide (now mostly empty) linked-snippet-lists relationships

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
• no new deprecations