[TASK] Add additional configuration for functional tests

Our functional test suit does not fail currently when
tested code emits a PHP warning. This is due to the
fact that the factory configuration uses the
production exception handler which silently discards
warnings.

This change adds additional configuration that
is merged with the factory configuration.

In this configuration the TYPO3 exception handling
is disabled and the core and classes cache is
disabled.

Additionally a new property is added to the base
class to easily add some configuration values that
might be needed for the test case.

Resolves: #56187
Related: #56086
Releases: 6.2
Change-Id: I5c7c2c0d495bae06a56d2285b8d521eaa4ab37d2
Reviewed-on: https://review.typo3.org/27773
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel