Move simple-update.yml from common to release directories

Based on the results from sylva-projects/sylva-core!5545 (merged), update-management-cluster is failing with:

2025/09/29 16:45:07.463597 HelmRelease/sylva-units state changed: UpgradeFailed - Helm upgrade failed for release sylva-system/sylva-units with chart sylva-units@0.0.0-git+6c06853f1fb3.4: values don't meet the specifications of the schema(s) in the following chart(s):
sylva-units:
- cluster: Additional property coredns is not allowed
2025/09/29 16:45:07.463680 Exiting as condition "reason" equals "UpgradeFailed" in unit HelmRelease/sylva-units, message: Helm upgrade failed for release sylva-system/sylva-units with chart sylva-units@0.0.0-git+6c06853f1fb3.4: values don't meet the specifications of the schema(s) in the following chart(s):
sylva-units:
- cluster: Additional property coredns is not allowed

This is because the additional key coredns from simple-update.yml is not being accepted by the schema. After discussing with @loic.nicolle, we agreed to move simple-update.yml from common to all release directories and current directory. For 1.3, the content of this file was modified, in order to overcome the issue that we initially faced.