Description of problem (please be detailed as possible and provide log
snippests):
Happens for both internal & external mode "Block & file" dashboard -
"Requested capacity" & "Utilization" (Used capacity) Cards only display data for default StorageClasses created by OCS operator (as part of StorageSystem creation). It do not include any custom StorageClasses (Ceph provisioned) which could be created by users as a day-2 operation. 

Version of all relevant components (if applicable): ODF 4.15 & ODF 4.15


Does this issue impact your ability to continue to work with the product
(please explain in detail what is the user impact)?
No (but dashboard should display complete information)


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 (ODF Block & file dashboards)

If this is a regression, please provide more details to justify this:
Yes (AFAIK earlier dashboards use to incorporate all ODF/OCS StorageClasses, default and custom).


Steps to Reproduce:
1. Deploy internal mode and external mode clusters (you can also deploy both on a same OCP, as ODF now supports multiple StorageClusters as well. Either is fine). 
2. Create some custom StorageClasses using ceph-rbd & ceph-fs provisioners.
3. Create PVC/PV using these custom and some default OCS StorageClasses.
4. Create some Pods and make sure these PVC/PV are attached/mounted to these "Running" pods (example: say we have 4 OCS StorageClasses/PVCs/PVs, we can create 4 Pods and mount each PVC to a separate Pod).
It's better if Pod can push some data to each PV, though not a hard requirement but good to do it before testing. Only hard requirement is that PVCs should be mounted, PVs should be bound and corresponding Pod should be running, otherwise "kubelet" metrics will not report this data at all.
5. Go to "Block & file" dashboard.
6. Check "Requested capacity" & "Utilization" (Used capacity) card, try different options from the dropdown.


Actual results: These cards only report capacity for the default OCS StorageClasses.


Expected results: It should report capacity for both default and custom created StorageClasses.


Additional info: PFA in the comments, this cluster had:
2 default & 1 custom "internal" PVs + PVCs, mounted to an active Pod.
1 default & 1 custom "external" PVs + PVCs, mounted to an active Pod.

1 default & 1 custom "internal" PVs + PVCs, not mounted to an active Pod.
1 default "external" PVs + PVCs, not mounted to an active Pod.

In attached screenshots we can see that,
for internal mode: Cards are only reporting 2 StorageClasses (default mounted ones), whereas it should report 3 ("2 default & 1 custom") in total.
for external mode: Cards are only reporting 1 StorageClass (default mounted), whereas it should report 2 ("1 default & 1 custom") in total.