Use apiextensions.k8s.io/v1 CustomResourceDefinition, rather than deprecated v1beta1

[jgwest]

The v1beta1 CRD definition is deprecated since Kubernetes v1.16, and is causing issues with the Helm chart linting, also described here.

This PR:

• Updates the makefile to generate v1 resources, rather than v1beta1
• Fixes issue with k8s behaviour in the metadata fields of a template, in generated CRD resource:
  • Since controller-gen intentionally doesn't generate validation for k8s.io/apimachinery/pkg/apis/meta/v1, it is not included in the OpenAPI CRD schema.
  • But, if using apiextensions.k8s.io/v1 then k8s APIServer doesn't recognize this field as a valid metadata field (outside of it's use at the root). When you try to create an ApplicationSet with .spec.template.metadata fields (for example, from kubectl), the APIserver ignores the values.
  • Solution is to split the supported fields into their own ApplicationSet-managed type, rather than relying on ObjectMeta type.

Fixes #127

[wtam2018]

LGTM
@jgwest thanks.