Rescope Implicit + Explicit Operators for Models

[jorgerangel-msft]

We currently generate both the implicit operation public static implicit operator BinaryContent(Friend friend) and the explicit operator public static explicit operator Friend(ClientResult result) for all models, minus unknown discriminator models. We should consider rescoping the generation of this to only generate the implicit operator for request models and the explicit operator for response models since there isn't a need to have these operators always generated.