Allow configuration to be mocked for behat tests

[bwaidelich]

For the routing Behat tests, we already allow to "simulate" custom site configurations.

For CR core tests, we allow custom Node Types to be configured.

Both approaches only work for the current request though.
It should be possible to change configuration for the whole lifecycle though, including sub requests (i.e. projections and catch up hooks)

[bwaidelich]

As discussed in our Neos 9 weekly, for Flow we might be able to actually store *.yaml files in a cache directory (for the current Application context) and make the Configuration Manager read those via Objects.yaml

[bwaidelich]

This will become obsolete with #4746