Support upgrade from 1.2.1 to main in CI

What does this MR do and why?

Change starting point of the upgrade to use 1.2.1

Remove capm upgrade scenario as it should not be necessary anymore

⚠️ This will require a reconfiguration of the scheduled pipeline to update: DEPLOYMENT_DESCRIPTION paremeter and match the new value

This MR will require new CI deployment values: sylva-projects/sylva-elements/ci-tooling/ci-deployment-values!134 (diffs)

New label ci-featuretest-upgrade-from-1.2.1 is created, I keep the same color scheme, but maybe we should change/delete the ancient label color to avoid confusion between them