Expose end-to-end module directory to test scripts

Several end-to-end tests access jars from modules in flink-end-to-end-tests.
To achieve this they use this hacky solutions like
$TEST_DATA_DIR/../../<module> or $TEST_INFRA_DIR/../../<module>.

This is brittle as hell can cause tests to fail by merely adding another directory layer.
We should instead export the flink-end-to-end directory in the pre-commit/nightly scripts.