[Rules migration][Integration test] Get migration rules API (elastic#…

…11232) (elastic#210867)

## Summary

[Internal link](elastic/security-team#10820)
to the feature details

Part of elastic/security-team#11232

This PR covers SIEM Migrations GET API (route:
`/internal/siem_migrations/rules/{migration_id}`) integration test:
* Basic calls
* Filtering
* Sorting
* Pagination