Re-implement a compatibliy layer for the original AcmeClient

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To support older users can we now create an AcmeClient that is marked as deprecated but implements the old api but which is backed by the new fluent api.

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we will need to retrieve the original unit tests to ensure the new AcmeClient api still works unchanged.

As we are not changing the AcmeClient api it will not support the new persistent dns auth flow.