Move CRD to v1

[ukclivecox]

• Will need to investigate Kubebuilder multi-version support.

[adriangonz]

Ideally, we want to to rename the current operator/pkg/apis/v1alpha2 package to operator/pkg/apis/v1. On top of this, we also want to list versions v1alpha2 and v1alpha3 (see #890).

[adriangonz]

It seems that the recommended way by kubebuilder to expose multiple versions is to have multiple packages, one per version. This is the approach taken by a few projects, including knative (https://github.com/knative/serving/tree/master/pkg/apis/serving).

In our case, to follow this pattern we would need to duplicate the apis/v1alpha2 folder into apis/v1alpha3 and apis/v1.

Note that these versions refer only to the SeldonDeployment CRD. Therefore, as new versions of Seldon Core come out, we could phase these deprecated packages/versions out. For example,

• v1.0 would have the three folders: v1alpha2, v1alpha3 and v1 (marking v1 for storage).
• v1.1 would phase out v1alpha2 and v1alpha3. Everyone on v1.0 would get encouraged to update to update their SeldonDeployment resources to v1 before upgrading to Seldon Core v1.1..

This seems to be the most straightforward solution, even though it involves duplicating code temporarily.