Deprecate metal3 units

Today two units are concerning metal3:

• the historical one https://gitlab.com/sylva-projects/sylva-core/-/blob/main/charts/sylva-units/values.yaml?ref_type=heads#L60
• the one provided by Suse https://gitlab.com/sylva-projects/sylva-core/-/blob/main/charts/sylva-units/values.yaml?ref_type=heads#L1770

The one provided by Suse is the default one, the historical one should be deprecated. The default one should then be renames "metal3".