Issue Description:
After the alteration of the custom resources handling behavior in #1851, there has been a breaking change.

1. GVRFromType is invariably invoked:

   kube-state-metrics/internal/store/builder.go

   Line 200 in 76f42c1

   gvr := util.GVRFromType(f.Name(), f.ExpectedType())

2. The subsequent function https://github.com/rexagod/kube-state-metrics/blob/25a1d8da057cf761d614c59a52785335d34082d1/pkg/util/utils.go#L143 puts forward a presumption that ExpectedType() persistently returns unstructured.Unstructured{}. This triggers panic if a different argument type is provided.

The change leads to a breaking compatibility with the previous interface that we use internally to enhance KSM with other metrics.

Moreover, the availableStore index now uses gvr.String() over ResourceName as per

Expected Outcome:
I anticipated ExpectedType() to have the capacity to return any resource type and f.Name() to serve as the resource index in availableStore.
Another solution would be to introduce a new function StoreIndex() or StoreName() in this interface.

Reproducibility Steps:
To reproduce this issue, simply add VPA as a custom resource and observe that the code triggers panic.

Additional Information:
None applicable.
Environment Details:
I'm using the kind cluster 1.27.1.

• Kube-state-metrics version: 2.10.0
• Kubernetes version (retrievable using kubectl version): 1.27.1
• Cloud provider or hardware setup: macOS ARM
• Any Other Relevant Information: