From<T> impl for serde types back to AWS types

[ielm]

serde_aws types currently implement From<T> to map aws-sdk types to serializable structs, but there is no current implementation for serde_aws types to the native aws-sdk types.

Because native types are non-exhaustive, the auto-implementation of Into is not satisfied and must be written manually.

This issue is a pre-req for publishing to crates.io.