NXCALS-3946 Spark server integration tests

Merge request template

COMPATIBILITY NOTE

Please make sure that this change is BACKWARDS COMPATIBLE and a new server will work correctly with clients using old APIs versions.

It may be that data sent in the new format will break the old clients.

In case of any potential incompatibility we have to inform our clients and schedule release & deployment with them.

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@acc-logging-team - please have a look for approval.

Integration tests for Spark Server and enhanced integration-tests.sh script to run base integration tests, thin api & python separately via options (no options = all run). A bug fixed on AvroToImmutableDataConverter (Utf8 returned from Avro instead of String).

Closes NXCALS-3946