DS-9452: Updates query to get collections referenced in the subscribers table

[nwoodward]

References

• Fixes Health check fails because subscriptions table no longer references collections directly #9452
• Related to Subscription feature rest #8620

Description

This small PR updates the SQL query to get collections with subscribers.

Instructions for Reviewers

1. Deploy this bug-fix branch
2. Have at least one subscription to a collection in the subscriptions table
3. Run [dspace]/bin/dspace healthcheck -e person@example.org
4. Observe that the health check completes successfully now and lists subscriptions in the output

Checklist

• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & integration tests). Exceptions may be made if previously agreed upon.
• My PR passes Checkstyle validation based on the Code Style Guide.
• My PR includes Javadoc for all new (or modified) public methods and classes. It also includes Javadoc for large or complex private methods.
• My PR passes all tests and includes new/updated Unit or Integration Tests based on the Code Testing Guide.
• If my PR includes new libraries/dependencies (in any pom.xml), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.
• If my PR modifies REST API endpoints, I've opened a separate REST Contract PR related to this change.
• If my PR includes new configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've linked them together.

[kanasznagyzoltan]

Without using DISTINCT or GROUP BY there isn't any duplicated row (duplicated collection)?

[nwoodward]

I didn't notice duplicates in my testing, but you're correct that it's easy to prevent them. I added the DISTINCT function.