docs: documented fetchCredentials options of JS SDK #34541

Job	Run time
setup	1m 56s
Shard (0) Unit Tests	9m 0s
integration-tests-packages	13m 50s
Shard (1) Unit Tests	5m 24s
Shard (0) HTTP Integration Tests	12m 18s
Shard (0) Module Integration Tests	11m 11s
Shard (1) HTTP Integration Tests	9m 10s
Shard (1) Module Integration Tests	9m 51s
unit-tests	1s
integration-tests-modules	1s
integration-tests-http	1s
	1h 12m 43s

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