Create Unit-Tests for Index Structures / GRPC

[silvanheller]

There are currently no tests which create index structures (e.g. PQ) via the GRPC endpoint and then query the corresponding columns. Apart from the obvious advantage to having tests, this would also provide developers with a clear example on which index structures are guaranteed to working if they are used just like in the tests.

The reason for this request is that the quick attempt of creating an index via CLI, rebuilding it and then querying the column did not work for the visualtextcoembedding entity in the V3C1 dump, but I did not get around to investigating the issue further.