Let users provide a custom deletion protection reason

[twobiers]

Currently, the function already provides a set of pre-defined reasons as per docs.

These reason strings appear in the Usage's spec.reason field and in deletion rejection messages, making it easy to understand why a resource cannot be deleted.

However, I think this statement is not yet fully true as it only indicates "who" protects from deleting and "where" the deletion protection was set - the "why" remains unclear as it is typically a decision done as to some functional requirement.
I believe it would be a good addition to add an additional annotation (or label) e.g. protection.fn.crossplane.io/reason so developers can pass context down to the usage.

apiVersion: ec2.aws.upbound.io/v1beta1
kind: VPC
metadata:
  annotation:
    protection.fn.crossplane.io/reason: |
      VPC is a critical component for our environment. Deletion would have a disastrous impact on our production environment. 
  name: my-vpc