[FEATURE] Implement Mediator types

[jhoogstraat]

Problem

It may not be desirable to always use CorvusModel for decoding the body of certain requests, like create or update requests.

Solution

To have more control over what the user is able to provide in a request body 'mediator', or 'carrier' types can be used.
These types are also refered to as 'Data Transfer Objects' or DTOs.
These can be implemented as DTOModifiers and ResponseModifier.

Alternative Solutions

Altering Create and Update endpoint to support these operations.
Altering CorvusModel to inherit this functionality.

[bmikaili]

I agree this is needed. I haven't figured out a way to solve this generically yet. I struggle to find a way to do it generically in CorvusModel itself. We may have to resort to how you did it in your pull request, where developers will have to manually extend their models.

[jhoogstraat]

My solution requires no changes to existing code, because by default nothing changes. By default the CorvusModel itself is used to decode create/update requests, just like before.

What do you have in mind? Somehow the developer has to tell the system, which properties to decode, no?

[bmikaili]

Yeah you're right. Currently in Swift there is probably no other way. If there was a way to iterate over the properties of a struct that implements a protocol it would be possible to do generically, but that's not something that can be done in Swift.

[PSchmiedmayer]

We will archive Corvus in favor of Apodini as a worthy successor.