[feat] [remove bundleless usge] use config instead of environment variables

[nikophil]

fixes #311

also related to #319

I don't really know if/how we should test this:

• unit test of DatabaseResetter (and ODM/ORM schema resetters) would be mocking hell
• functional test would require several connections/objet managers, which really feels over-engineered...

Even testing the configuration would be tricky. I usually use a KernelBuilder for this.

WDYT?

[nikophil]

about the test stuf, maybe a quick win would be to name our connections / managers with another name than "default" use this name in the config

[kbond]

If not explicitly setting the connections/managers, does it use default or run on all available connections/managers?

[nikophil]

we're using default names: $this->registry->getDefaultConnectionName(), $this->registry->getDefaultManagerName()

[kbond]

Ah, ok, hah - if we add a non-default connection/manager to the config for the tests, we lose the test for choosing the defaults... Let's leave untested for now - I don't want yet another test permutation. Of course, if there's a reported issue, we can re-evaluate.

[nikophil]

ok, hopefully we'll remove 5 or more test permutation after USE_FOUNDRY_BUNDLE usage will be removed