Introduce label selector based class scheduling

[negz]

Description of your changes

This enables label based class matching per #926. Changes will also be required to crossplane, and all stacks.

Checklist

I have:

• Run make reviewable to ensure this PR is ready for review.
• Ensured this PR contains a neat, self documenting set of commits.
• Updated any relevant documentation, examples, or release notes.
• Updated the RBAC permissions in clusterrole.yaml to include any new types.

[hasheddan]

This looks great! Cross-checked with the stated design and feels like it adheres. None of my comments are blocking so I will go ahead and approve, but also will be looking for the first stack implementation to review. Awesome work :)

[hasheddan]

Do you know what happens if we try and set this owner reference?

[negz]

I haven't looked at this for some time, but as far as I can tell it works. Currently we almost always dynamically provision a managed resource in a separate namespace from the resource claim, yet deleting the resource claim automatically deletes the managed resource (via owner reference based garbage collection).

What's interesting is that I have no idea how this works - I'm not sure how the garbage collector figures out what to delete without knowing the owner's namespace.

[hasheddan]

I am going to dive into this a little bit more, but I don't think my investigation needs to block here :)

[negz]

Here's an example of simple resource class selection in action:

$ kubectl get redisclass -l classy="true"
NAME                     PROVIDER-REF   RECLAIM-POLICY   AGE
azure-redis-labelled-a   example        Delete           51m
azure-redis-labelled-b   example        Delete           51m
azure-redis-labelled-c   example        Delete           51m
azure-redis-labelled-d   example        Delete           51m
azure-redis-labelled-e   example        Delete           51m

$ kubectl get cloudmemorystoreinstanceclass -l classy="true"
NAME                   PROVIDER-REF   RECLAIM-POLICY   AGE
gcp-redis-labelled-a   example        Delete           50m
gcp-redis-labelled-b   example        Delete           49m
gcp-redis-labelled-c   example        Delete           49m
gcp-redis-labelled-d   example        Delete           49m
gcp-redis-labelled-e   example        Delete           49m

$ kubectl get rediscluster
NAME          STATUS   CLASS-KIND                      CLASS-NAME               RESOURCE-KIND              RESOURCE-NAME               AGE
app-redis-0            RedisClass                      azure-redis-labelled-b   Redis                      default-app-redis-0-8rhkr   4m31s
app-redis-1            RedisClass                      azure-redis-labelled-b   Redis                      default-app-redis-1-tbn7g   4m11s
app-redis-2            CloudMemorystoreInstanceClass   gcp-redis-labelled-a     CloudMemorystoreInstance   default-app-redis-2-mrqpm   3m52s
app-redis-3            RedisClass                      azure-redis-labelled-c   Redis                      default-app-redis-3-glr4s   3m36s
app-redis-4            RedisClass                      azure-redis-labelled-b   Redis                      default-app-redis-4-vdzc9   3m27s
app-redis-5            CloudMemorystoreInstanceClass   gcp-redis-labelled-b     CloudMemorystoreInstance   default-app-redis-5-2qt5r   3m20s
app-redis-6            RedisClass                      azure-redis-labelled-a   Redis                      default-app-redis-6-t7g59   3m11s
app-redis-7            CloudMemorystoreInstanceClass   gcp-redis-labelled-a     CloudMemorystoreInstance   default-app-redis-7-cwmpl   2m25s
app-redis-8            CloudMemorystoreInstanceClass   gcp-redis-labelled-b     CloudMemorystoreInstance   default-app-redis-8-9dcm4   2m25s
app-redis-9            CloudMemorystoreInstanceClass   gcp-redis-labelled-b     CloudMemorystoreInstance   default-app-redis-9-fdxqf   2m25s

The claims are all variants of:

---
apiVersion: cache.crossplane.io/v1alpha1
kind: RedisCluster
metadata:
  name: app-redis-0
spec:
  classSelector:
    matchLabels:
      classy: "true"
  writeConnectionSecretToRef:
    name: app-redis-0