[resource/codegen] Make resource.Object compatible with kuberenetes

[Austin Pond]

Currently, kubernete's go APIs expect runtime.Object for most things, which, under the hood, are expected to be more complete interfaces (such as schema.ObjectKind and metav1.Object). The interface used by the app-sdk should be a superset of what is required by kubernetes, so that all objects used in the app-sdk can be used with the kubernetes go APIs unchanged. An example of how the resource.Object interface should be modified:

type Object interface {
    runtime.Object // Baseline k8s interface, requires DeepCopyObject and Destroy
    schema.ObjectKind // Provides GVK information
    metav1.Object // Provides all the Object metadata methods
    // ...Other methods as required by the app-sdk...
}

Additionally, as part of this, unmarshal logic should be removed from the resource.Object interface, and moved into a separate type which can handle an input of raw bytes and output a typed or untyped resource.Object. This is analogous to an extended version of resource.Schema, which also can marshal/unmarshal. A proposed solution for this looks like:

type Kind struct {
    Schema
    Codecs map[resource.KindEncoding]Codec
}

type Codec interface {
    Read(in io.Reader, into Object) error
    Write(out io.Writer, from Object) error
}