Description of problem (please be detailed as possible and provide log
snippests):

[Requires backport]
"Custom storage classes are not supported for external mode OpenShift Data Foundation clusters." - https://docs.redhat.com/en/documentation/red_hat_openshift_data_foundation/4.16/html-single/managing_and_allocating_storage_resources/index#storage-classes_rhodf

We have a web page that offers a form to create Storage Class on Multi-StorageCluster deployments

Version of all relevant components (if applicable):
OCP 4.17.0, ODF 4.17.0-124

Does this issue impact your ability to continue to work with the product
(please explain in detail what is the user impact)?
web page misleads

Is there any workaround available to the best of your knowledge?
no

Rate from 1 - 5 the complexity of the scenario you performed that caused this
bug (1 - very simple, 5 - very complex)?

Can this issue reproducible?
yes

Can this issue reproduce from the UI?
yes

If this is a regression, please provide more details to justify this:

Steps to Reproduce:
1. Deploy External mode deployment or MultiStorageCluster deployment and login
2. Navigate to Storage / StorageClasses / Create StorageClass
3.

Actual results:
User is allowed to fill the form but can not pick Storage Pool, no dropdown on mandatory field. That creates feeling of a broken UI. User is not notified that create Storage Class using external storage is not allowed.

Expected results:
User is not allowed to create Storage Class and fill the form, when Storage system is external and notified that create Storage Class using external storage is not allowed

Test logs:
https://url.corp.redhat.com/17c72a1

must-gather logs:
https://url.corp.redhat.com/ca8f684

Additional info:
If no UI solution to restrict User and disable fields, user should be at least notified about existing restrictions