[RFE] Implement validation logic to check if cloud credentials are valid for RKE2/K3S clusters

[markusewalker]

Is your feature request related to a problem? Please describe.

When using the rancher2 provider to provision RKE2/K3S node driver/custom clusters, there is currently no check on ensuring that cloud credentials are valid. As a result, the cluster will begin to provision, however, the nodes are in a cycle where they're constantly deleting themselves as shown below:

Providing the correct credentials fixes this issue and the downstream RKE2/K3S provision successfully.

Describe the solution you'd like

We should implement a check where there is a validation performed for cloud credentials. In the Rancher UI, there is a validation check that does not allow you create a bogus cloud credential.