feat: optional base64 encoding for local cred #502

Job	Run time
Collect changes / collect-changes	6s
Python tests / lint-and-format-check	42s
Python tests / types-check	1m 3s
Python tests / unit-tests (py313)	3m 5s
Python tests / unit-tests (py312)	3m 27s
Python tests / unit-tests (py311)	2m 23s
Python tests / unit-tests (py310)	2m 12s
Python tests / unit-tests (py39)	2m 35s
status-check	2s
	15m 35s

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