Handle when response is a file URL in AlamofireDecodableRequestBuilder.

[RedDragonJ]

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Description of the PR

@ehyche
This is the equivalent change in the AlamofireDecodableRequestBuilder to the change which was made in the non-decodable request in this PR:

#6469

This updates AlamofireImplementations.mustache to handle when the response is an URL. It also makes changes in the generated sample code for:

default configuration (no promisekit or rxswift)
promisekit
rxswift