Clean up credentials related code

Credentials are used by BackupStorageLocation (BSL) and VolumeSnapshotLocation (VSL)

• confirm that no other part of OADP uses credentials code
• should controllers/registry.go be deleted/moved to pkg/credentials/credentials.go?

in controllers/bsl.go

• https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L72-L74 is duplication of https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L415

• https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L81-L83 is duplication of https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L386

• these functions all have duplication
  https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L268
  https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L299
  https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L330

  move it to this function https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L361 (but remove secret validation from it, it already done by other part of the code)

• should this only be called if !(dpa.Spec.Configuration.Velero.HasFeatureFlag("no-secret"))? https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L123-L127

• remove validation from this function, it was done previously https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/bsl.go#L194

in controllers/registry.go

• are not these duplication from api/v1alpha1/oadp_types.go? https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/registry.go#L55
• this function should not patch secret every time https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/registry.go#L216 move patching code to validation part
• delete this code https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/registry.go#L264-L270 and docs/developer/testing/ MULTI_CLOUD_TESTING_UPDATES.md file
• verify credential function should check all cases

// add doc comments!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
func (r *DPAReconciler) verifyCredential(credential *corev1.SecretKeySelector, provider oadpv1alpha1.DefaultPlugin, location string) error {
	var credentialName string
	var credentialKey string

	if credential != nil {
		// Check if user specified empty credential name
		if credential.Name == "" {
			return fmt.Errorf("credential name specified in %s cannot be empty", location)
		} else {
			credentialName = credential.Name
		}
		// Check if user specified empty credential key
		if credential.Key == "" {
			return fmt.Errorf("credential key specified in %s cannot be empty", location)
		} else {
			credentialKey = credential.Key
		}
	} else {
		if provider != "" {
			// Assume default values
			credentialName = credentials.PluginSpecificFields[provider].SecretName
			credentialKey = credentials.PluginSpecificFields[provider].PluginSecretKey
		} else {
			// cloud storage case
			return fmt.Errorf("must provide a valid credential secret")
		}
	}

	secret, err := r.getProviderSecret(credentialName)
	if err != nil {
		return err
	}
	// need???
	// if secret.Name == "" {
	// 	return false, errors.New("secret not found")
	// }
	data, foundKey := secret.Data[credentialKey]
	if !foundKey || len(data) == 0 {
		return fmt.Errorf("Secret name %s is missing data for key %s", credentialName, credentialKey)
	}
	return nil
}

in controllers/validator.go

• delete this function https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/validator.go#L74 credentials should have been already validated previously

in controllers/vsl.go

• duplication from controllers/registry.go https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/vsl.go#L18
• duplication from function pluginExistsInVeleroCR in controllers/bsl.go https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/controllers/vsl.go#L256

in pkg/credentials/credentials.go

• delete https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/pkg/credentials/credentials.go#L77
• delete https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/pkg/credentials/credentials.go#L358 duplication from registry.go
• remove duplication in https://github.com/openshift/oadp-operator/blob/91e1aacf47ea2b44bafdb9d6d3c14ffee6907baf/pkg/credentials/credentials.go#L389

Start by tracing credential handling across controllers/bsl.go, controllers/registry.go, controllers/validator.go, controllers/vsl.go, pkg/credentials/credentials.go, and api/v1alpha1/oadp_types.go. Review the linked locations and existing validation paths first; done means the listed duplication, unnecessary patching, obsolete code, and credential-checking gaps have been resolved consistently across BSL and VSL.