Disallow creation of ResourceGroups if value of immutable field is invalid

[amirahav]

Description

Observed Behavior:
kro currently allows a ResourceGroup with an invalid value of an immutable field to be created.
This then requires the deletion and recreation of the ResourceGroup.

Expected Behavior:
The kro controller returns an error and doesn't create the ResourceGroup.

Reproduction Steps (Please include ResourceGroup and Instances files):

apiVersion: kro.run/v1alpha1
kind: ResourceGroup
metadata:
  name: sqs-queue
spec:
  schema:
    apiVersion: v1alpha1
    kind: sqs-queue
    spec:
      ...

Versions:

• kro version:
• Kubernetes Version (kubectl version):

Involved Controllers:

• Controller URLs and Versions (if applicable):
• kro v0.1.0

Error Logs (if applicable)**:

Paste any relevant logs here

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