vSphere provider thumbprint required by EKS-A controller when insecure set

**What happened**

When creating vSphere clusters with the EKS-A controller and `insecure=true` in the datacenter config, the controller still requires the thumbprint.

**What do you expect?**

When specifying `insecure=true` for vSphere cluster creation the EKS-A controller doesn't require a thumbprint.

Start at the EKS-A controller's vSphere cluster-creation path and its datacenter configuration handling. Reproduce creation with insecure=true and no thumbprint, then trace where the thumbprint is required. Done means an insecure vSphere configuration no longer requires a thumbprint while other configurations retain their expected validation.

Written by the indexing model from the issue text.