add Singularity support for "dockerFile" #1939

Job	Run time
Linters (lintreadme)	54s
Linters (shellcheck)	13s
Linters (pydocstyle)	21s
Tox (3, 8, lint)	32s
Tox (3, 8, unit)	6m 34s
build_test_container	9m 42s
Tox (3, 8, bandit)	33s
Tox (3, 8, mypy)	8m 31s
Tox (3, 9, lint)	26s
No leftovers	5m 5s
Tox (3, 9, unit)	7m 15s
Tox (3, 9, bandit)	24s
CWL conformance (v1.0, docker)	3m 35s
Tox (3, 9, mypy)	8m 5s
cwltool release test	16m 9s
CWL conformance (v1.0, singularity)	3m 21s
Tox (3, 10, lint)	29s
CWL conformance (v1.0, podman)	3m 35s
Tox (3, 10, unit)	7m 17s
CWL conformance (v1.1, docker)	4m 50s
Tox (3, 10, bandit)	28s
CWL conformance (v1.1, singularity)	7m 4s
Tox (3, 10, mypy)	8m 33s
CWL conformance (v1.1, podman)	5m 13s
CWL conformance (v1.2, docker)	6m 52s
Test on macos-latest	12m 32s
CWL conformance (v1.2, singularity)	6m 59s
CWL conformance (v1.2, podman)	7m 9s
CWL conformance (v1.2, docker, --fast-parser)	7m 7s
Tox (3, 11, lint)	34s
Tox (3, 11, unit)	7m 5s
Tox (3, 11, bandit)	33s
Tox (3, 11, mypy)	7m 27s
Tox (3, 12, lint)	30s
Tox (3, 12, unit)	8m 40s
Tox (3, 12, bandit)	34s
Tox (3, 12, mypy)	9m 16s
	3h 4m 27s

Provide feedback