Document how to update vSphere thumbprint

**What would you like to be added**:
Documentation around how cluster admins to update vSphere thumbprint in the management and workload EKS Anywhere clusters.

**Why is this needed**:
EKS Anywhere currently supports updating the vSphere thumbprint using the `eksctl upgrade command` but there are no docs around how to do it. Since this is not a trivial process, well documented steps on how to update this field would be really beneficial.

Start by locating the documentation for the eksctl upgrade command and the existing vSphere thumbprint upgrade behavior. Document the steps cluster administrators need to update the thumbprint in both management and workload EKS Anywhere clusters, with completion shown by clear instructions for each cluster type.

Written by the indexing model from the issue text.