Add option to disable env var interpolation in configs #1178

Job	Run time
Run tests with different pydantic versions	3m 45s
Run tests on legacy versions (3.7)	2m 8s
Run linters (flake8)	1m 49s
Run linters (pydocstyle)	1m 45s
Run tests with coverage	2m 59s
Run tests (3.8)	2m 4s
Run linters (mypy)	1m 55s
Run linters (pylint)	1m 47s
Run tests (3.9)	2m 2s
Run tests (3.10)	2m 4s
Run tests (3.11)	2m 6s
Run tests (3.12)	2m 6s
Run tests (3.13)	2m 7s
	28m 37s

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