PTEUDO-1990: Prevent deletion requests DatabaseClaim CRs

[bfabricio]

Use a label to validate deletions of DatabaseClaim. A validating webhook will look for the presence or absence of this field to allow the deletion. If a user attempts to delete the CR, it will fail the request with a notice about the label requirement.

$ kubebuilder create webhook --version v1 --kind DbRoleClaim --group persistance --programmatic-validation
$ kubebuilder create webhook --version v1 --kind DatabaseClaim --group persistance --programmatic-validation