Adding a note in all the relavant docs regarding default vSAN policy in the Storage class

**What would you like to be added**:
We should add a note in all the relevant EKS Anywhere docs such as [here](https://anywhere.eks.amazonaws.com/docs/workshops/packages/prometheus/prometheus_grafana/) regarding the default storage class with the vSAN Storage Policy.

**Why is this needed**:
This would help anyone trying to follow the docs to be aware of the default storage class and if they have to create any new policy for a storage class. This will also help reduce the time in debugging issues related to having a default storage class.

Start with the Prometheus/Grafana workshop page linked in the issue and inspect the surrounding EKS Anywhere documentation for references to the default storage class and vSAN Storage Policy. Done means the relevant docs consistently explain the default storage class and whether a new policy is needed.

Written by the indexing model from the issue text.