[1.1.0-CI] backport schema change for sylva_diskimagebuilder_images

!2460 (merged) introduced a new behavior on how are tested the upgrades from 1.1.0 to main: the environment values are now in https://gitlab.com/sylva-projects/sylva-elements/ci-tooling/ci-deployment-values. When doing that, we didn't realize that some of those values (new ones introduced byhttps://gitlab.com/sylva-projects/sylva-elements/ci-tooling/ci-deployment-values/-/merge_requests/2/diffs?commit_id=ce8dbc101e2aa196eafa768715765847518442f0) require a sylva-units schema update. This update was introduced in main but is also needed "in 1.1.0".

This MR here is introducing this schema update in a 1.1.0-ci-tweaks new branch, forked right from 1.1.0 tag. Using this branch in the scheduled job testing the upgrade from 1.1.0 to main.

This should solve this issue seen in https://gitlab.com/sylva-projects/sylva-core/-/jobs/7149617552

sylva-units:
- sylva_diskimagebuilder_images: Property name of "{{ .Values._internal.image_key }}" does not match
- sylva_diskimagebuilder_images: Does not match pattern '^[a-z0-9][a-z0-9-]{1,50}[a-z0-9]$'