Add ActorTemplate and ActorTemplateVersion as substrate resources

[Zoe Zhao (zoez7)]

Part of #477 . Adding both AT and ATV as global resources in substrate.

All ATV fields are immutable. SandboxConifg will be frozen into ATV at creation time.

• Tests pass

• Appropriate changes to documentation are included in the PR.

Not yet, will add documentation once we cut over from the the current CRD impl.

Demo: what the counter demo will look like with AT and ATV:

apiVersion: api.ate.dev/v1alpha1
kind: ActorTemplate
metadata:
  name: counter-atv
spec:
  workerSelector:
    matchLabels:
      workload: counter
  defaultVersionOnCreate:
    name: counter-atv-v1
---
apiVersion: api.ate.dev/v1alpha1
kind: ActorTemplateVersion
metadata:
  name: counter-atv-v1
actorTemplate:
  name: counter-atv
spec:
  pauseImage: "registry.k8s.io/pause:3.10.2@sha256:f548e0e8e3dc1896ca956272154dde3314e8cc4fde0a57577ee9fa1c63f5baf4"
  containers:
  - name: counter
    image: ko://github.com/agent-substrate/substrate/demos/counter
    command:
    - /ko-app/counter
    env:
    - name: VERSION
      value: v1
    readyz:
      httpGet:
        path: /readyz
        port: 80
    volumeMounts:
    - name: data
      mountPath: /home/counter
  volumes:
  - name: data
    durableDir: {}
  snapshotsConfig:
    onPause: SNAPSHOT_CONTENT_SCOPE_FULL
    onCommit: SNAPSHOT_CONTENT_SCOPE_DATA
    storageLocation: gs://${BUCKET_NAME}/ate-demo-counter-atv/
  sandboxConfig:
    sandboxClass: SANDBOX_CLASS_GVISOR
    configName: gvisor-default
---

[Haven Xia (HavenXia)]

As discussed offline ActorTemplateSpec will be flatten into ActorTemplate.

[Zoe Zhao (zoez7)]

I tried to stack PR reviews on top of each other, and failed. Closing this PR. Will use #824 to review these changes.