Resource leakage PoC

[seregamorph]

Track used resources between integration test execution:

• heap memory
• number of active threads

TODO add sensors:

• number of opened file descriptors
• distinguish server and client network connections
• number of active docker containers by testcontainers
• number of loaded classes(?)

Optionally after each test group that share the same config (and accordingly context) it's possible to opt-in call of System.gc() via option -Dtestsmartcontext.handleAfterClassGroup.gc=true. Usually it's a bad practice, but for the sake of better heap reports this can give better clarity, so makes sense to use from time to time.