fix(dspy): add copy to AzureOpenAI to propagate api_(key|version|...)

[snimu]

Fixes issue #591 without re-creating issue #543

The problem was that AzureOpenAI.copy used LM.copy, but because api_key etc. aren't in the AzureOpenAI.kwargs, and LM.copy per default only propagates self.__class__.kwargs.

I now gave AzureOpenAI its own copy-method. This isn't really beautiful, but it seems to work pretty well.

[arnavsinghvi11]

Thanks @snimu !