Remove cluster_public_endpoint from values

What does this MR do and why?

Remove cluster_public_endpoint from values

This parameter was added to management-cluster-values as we were foreseeing to use it later-on to address #570 (closed).

But it remains unused so far, and @tmmorin observed that it was triggering a useless additional reconciliation of sylva-units in bootstrap

In order to support upgrades without, we also have to remove the valueFrom/configmap from previous sylva-units Helmreleases otherwise it would break the new schema

Closes #1588