feat(GAT-6611): PoC nested dataset subtype filters

[BSnelling]

Screenshots (if relevant)

Describe your changes

Issue ticket link

https://hdruk.atlassian.net/browse/GAT-6173

Environment / Configuration changes (if applicable)

Requires migrations being run?

If not using the pre-push hook. Confirm tests pass:

Checklist before requesting a review

• I have performed a self-review of my code
• I have added appropriate unit tests
• I have created mocks for unit tests (where appropriate)
• I have added appropriate Behat tests to confirm AC (if applicable)
• I have added Swagger annotations for new endpoints (if applicable)
• I have added audit logs for new operation logic (if applicable)
• I have added new environment variables to the .env.example file (if applicable)
• I have added new environment variables to terraform repository (if applicable)

[github-actions]

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