DigitizationTestsMT: Add two AthenaMP SharedWriter Digitization ART tests
This MR adds two digitization ART tests akin to test_Digi_tf_mc20e_MP_reproducibility.sh in which we test the functionality of SharedWriter w/ and w/o parallel compression (i.e. legacy mode) in vanilla AthenaMP as well as fork-after-first-event. The tests are confirmed to succeed locally with master/2022-03-02T2101.