Handle Baremetal registrymirror upgrade validation

**What happened**:
We do not upgrade registry mirror configuration for BareMetal provider.

**What you expected to happen**:
Pre-flight validation stating registry mirror fields are not mutable or with the in-place upgrade functionality for tinkerbell, these fields should be mutable.

**How to reproduce it (as minimally and precisely as possible)**:
1. Create a Bare metal cluster with registry mirror configuration.
2. Upgrade with the changed registry mirror fields.
3. Upgrade succeeds without changing registry mirror config values.

**Anything else we need to know?**:

**Environment**:
- EKS Anywhere Release:
- EKS Distro Release:

Start by reproducing the Bare Metal upgrade with changed registry mirror fields, then trace the upgrade and pre-flight validation paths for registry mirror configuration. Compare the current behavior with the expected handling for Bare Metal and Tinkerbell, and verify that the completed behavior either reports immutability clearly or applies the fields during an in-place upgrade.

Written by the indexing model from the issue text.