Update the integration test framework to test different combinations of data loading/retrieval mechanisms

[t616178]

Currently, there are some gaps in the integration test framework around testing combinations of data loading and retrieval mechanisms. This gap should be closed by extending the existing integration test framework with additional tests which test for correct operation using all available combinations of loading and data retrieval mechanisms for each store type.

[m55624]

This ticket has now been split into two branches, gh-1657-loader-tests and gh-1657-flink-IT-tests. This is because there has been issues with the ITs in the flink library. When gh-1657-loader-tests has been merged https://github.com/gchq/Gaffer/issues/1833 can go ahead using the TestSchema class.

[d47853]

Merged into develop

[m55624]

There is still gh-1657-flink-IT-tests branch to fix under this ticket.

[n3101]

@m29827 I see you did Improve Kafka flink tests #2325 Are you able to tell whether your changes cover this comment above: "There is still gh-1657-flink-IT-tests branch to fix under this ticket." ??

[m29827]

@m29827 I see you did Improve Kafka flink tests #2325 Are you able to tell whether your changes cover this comment above: "There is still gh-1657-flink-IT-tests branch to fix under this ticket." ??

The work for gh-2325 didn't add any new coverage to the Flink tests, it removed unpredictability in their execution which caused intermittent failures. The gh-1657-flink-IT-tests branch hasn't been updated since 2019, I don't know if it's related or not.