allow pool creation even if the referenced image doesn't exist yet

[bavarianbidi]

What is the feature you would like to have?

At the moment it's not possible to create a pool CR when the referenced image CR doesn't exist.
This might cause some confusion as you have to need to know that the image must exist before a pool got created.

The common pattern for such cases in kubernetes is to requeue the reconciliation and try again.

• a pool CR can be created even if the referenced image doesn't exist
• once the referenced image CR got created, the pool get created in garm
• image update still works (updating the tag in the image-cr will update all pools where the image is used)

Anything else you would like to add?

Similar to a pod spec it's possible to create a pod, even if the referenced image isn't available in the registry.
The pod controller is reconciling the pod-creation (with an exponential backoff) and once the image is available in the registry, the pod got scheduled.

[rafalgalaw]

closed with #76