fix: fixed autoscaling with the hpa

[TomerFi]

Added a Resources field to the WildFlyServerSpec type.

This will allow the user to specify the CPU requirement for containers,
which is mandatory for the HPA calculation of CPU utilization.

Example of HPA eligible application:

apiVersion: wildfly.org/v1alpha1
kind: WildFlyServer
metadata:
  name: quickstart
spec:
  applicationImage: "quay.io/wildfly-quickstarts/wildfly-operator-quickstart:18.0"
  replicas: 2
  resources:
    requests:
      cpu: "0.5"

---

Added a string Selector field of type string to the WildFlyServerStatus type.

This will be used for storing the selector label which is populated by the operator with the key app.kubernetes.io/instance.
The value for the label is created from the prefix wildfly- concatenated with the application name.
The same label is also applied to the underlying containers via the StatefulSet's template.

This is required for targeting the CR with the HPA instead of the underlying StatefulSet,
which is required to maintain the CR as the source for any of its resources.

[jmesnil]

Aside from my comment on the label, this looks good.

Thanks a lot for fixing this issue!

[jmesnil]

Looks good to me, thanks!

[jmesnil]

This fixes #208 & #211

[BobVanB]

Good evening, any progress with this pull request?

[jmesnil]

I'm closing your PR as it has been merged in the aggregated PR #215. Thanks!