Add deprecation warning for `TemplatedConfigLoader` and `ConfigLoader` #11

Job	Run time
e2e-tests (ubuntu-latest, 3.8) / e2e-tests	15m 37s
e2e-tests (ubuntu-latest, 3.10) / e2e-tests	12m 5s
e2e-tests (ubuntu-latest, 3.7) / e2e-tests	14m 38s
e2e-tests (windows-latest, 3.10) / e2e-tests	21m 49s
e2e-tests (ubuntu-latest, 3.9) / e2e-tests	13m 27s
e2e-tests (windows-latest, 3.7) / e2e-tests	27m 13s
e2e-tests (windows-latest, 3.8) / e2e-tests	27m 0s
e2e-tests (windows-latest, 3.9) / e2e-tests	25m 27s
lint (ubuntu-latest, 3.10) / lint	7m 40s
unit-tests (ubuntu-latest, 3.10) / unit-tests	16m 56s
unit-tests (ubuntu-latest, 3.7) / unit-tests	16m 50s
unit-tests (ubuntu-latest, 3.8) / unit-tests	6h 0m 14s
unit-tests (ubuntu-latest, 3.9) / unit-tests	15m 14s
unit-tests (windows-latest, 3.10) / unit-tests	25m 39s
unit-tests (windows-latest, 3.7) / unit-tests	22m 58s
unit-tests (windows-latest, 3.9) / unit-tests	19m 50s
unit-tests (windows-latest, 3.8) / unit-tests	26m 25s
	11h 9m 2s

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