Refactor level2 to eliminate the input_sink and set all input defaults in the top group's configure method. #467

Job	Run time
pre_commit	15s
test_ubuntu (oldest, 3.9, 1.20, 1.6, v2.9.1, 7.7, dev, 1.8.0, 0, 0)	15m 8s
test_ubuntu (dev, 3, 1, 1, v2.9.1, 7.7, dev, dev, 0, 0)	15m 19s
test_ubuntu (latest, 3.10, 1, 1, v2.9.1, 7.7, dev, latest, 0, 0)	14m 5s
test_ubuntu (latest_docs, 3, 1, 1, v2.9.1, 7.7, dev, latest, 1, 0)	12m 45s
test_ubuntu (latest_benches, 3, 1, 1, v2.9.1, 7.7, latest, latest, 0, 1)	6m 19s
	1h 3m 51s

Provide feedback