Add migration steps for `ConfigLoader` to `OmegaConfigLoader` #206

Job	Run time
e2e-tests (ubuntu-latest, 3.10) / e2e-tests	14m 48s
e2e-tests (ubuntu-latest, 3.7) / e2e-tests	12m 9s
e2e-tests (ubuntu-latest, 3.8) / e2e-tests	14m 28s
e2e-tests (ubuntu-latest, 3.9) / e2e-tests	14m 40s
e2e-tests (windows-latest, 3.10) / e2e-tests	23m 19s
e2e-tests (windows-latest, 3.8) / e2e-tests	23m 26s
e2e-tests (windows-latest, 3.7) / e2e-tests	27m 43s
e2e-tests (windows-latest, 3.9) / e2e-tests	21m 46s
lint (ubuntu-latest, 3.10) / lint	3m 47s
pip-compile (ubuntu-latest, 3.10) / pip-compile	4m 40s
pip-compile (ubuntu-latest, 3.7) / pip-compile	5m 31s
pip-compile (ubuntu-latest, 3.8) / pip-compile	4m 42s
pip-compile (ubuntu-latest, 3.9) / pip-compile	3m 53s
pip-compile (windows-latest, 3.10) / pip-compile	8m 12s
pip-compile (windows-latest, 3.7) / pip-compile	11m 11s
pip-compile (windows-latest, 3.8) / pip-compile	11m 5s
pip-compile (windows-latest, 3.9) / pip-compile	8m 41s
unit-tests (ubuntu-latest, 3.10) / unit-tests	18m 26s
unit-tests (ubuntu-latest, 3.7) / unit-tests	14m 27s
unit-tests (ubuntu-latest, 3.8) / unit-tests	12m 41s
unit-tests (ubuntu-latest, 3.9) / unit-tests	16m 21s
unit-tests (windows-latest, 3.10) / unit-tests	25m 50s
unit-tests (windows-latest, 3.7) / unit-tests	21m 23s
unit-tests (windows-latest, 3.8) / unit-tests	18m 20s
unit-tests (windows-latest, 3.9) / unit-tests	18m 1s
	5h 59m 30s

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