Closes #512 - Test KadaiEngine with different ConnectionManagementModes

[bruderj15]

Tests for ConnectionManagementMode=PARTICIPATE are not yet complete.

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[bruderj15]

ConnectionManagementMode=EXPLICIT succeeds with H2 and Postgres but fails with DB2, see CI.

Seems like a bug with DB2.
Having no knowledge about DB2 at all, I cannot find it.

[CRoberto1926]

You could probably summarize KadaiEngineAutocommitModeTest, KadaiEngineExplicitModeTest and KadaiEngineParticipateModeTest in one KadaiEngineModesTest class, and then group them using @Nested. I think they would be better grouped together.

[bruderj15]

Wondering big time here.
Current failures are:

• EXPLICIT succeeds with H2 and Postgres but fails with DB2, see CI
• PARTICIPATE fails completely, see CI

[bruderj15]

@jamesrdi you are familiar with the core, right? What's going wrong here?