Use encrypted dns proxy in `mullvad-ios` #477

Job	Run time
build-ios (aarch64-apple-ios)	2m 3s
build-ios (aarch64-apple-ios-sim)	1m 58s
clippy-check-ios (aarch64-apple-ios)	1m 7s
clippy-check-ios (aarch64-apple-ios-sim)	1m 8s
	6m 16s

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