Combine PagingQueryEmbeddedMongoTest and PagingQueryRealMongoTest

[sleberknight]

Both PagingQueryEmbeddedMongoTest and PagingQueryRealMongoTest are tests of PagingQuery. The only reason PagingQueryRealMongoTest exists is because the in-memory de.bwaldvogel.mongo.MongoServer.MongoServer that we use for other Mongo testing does not work when testing the PagingQuery#aggregatePage (it throws a NPE).

We used the "flapdoodle" embedded Mongo for this one test. Recently the flapdoodle embedded Mongo (3.5.x) was completely re-written and released as version 4.1.0. Unfortunately, they completely changed the API, so with version 4.1.0, PagingQueryEmbeddedMongoTest no longer even compiles. It seems like a better option to simply replace it than try to learn an entire new API for literally just one test class.

Another issue is that the PagingQueryRealMongoTest must be run manually which pretty much means it never gets run.

So, using Testcontainers, we can combine PagingQueryEmbeddedMongoTest and PagingQueryRealMongoTest into a single test and use Testcontainers. In addition, we should be able to design the test so that it runs against different versions of Mongo, e.g. 3, 4, 5, and 6.

Once we combine these tests, we can remove the dependency on flapdoodle (and then also remove from kiwi-bom since we don't use flapdoodle anywhere else in our libraries or services).

[sleberknight]

Removing the milestone for now. This isn't a high priority at the moment, so will revisit later.