Convert definition composite-aggregation performance tests to functional tests

Context:
With OPT-3428 we introduced `*_canHandleOver10kDefinitions` tests to verify that the composite aggregations to retrieve definitions work correctly and perform. This however does not properly work for the nightly AWS Elastic integration step as this has a way higher network latency and general performance.

We thus should convert these IT's to purely functional tests configuring a custom `search.max_buckets` setting (e.g. 1000) for the scope of these tests and just verifying that all definitions are returned.

For Performance tests we should extend the `QueryPerformanceTest` class with corresponding tests