build: cern-magnum is packaged as two seperate helm charts

From discussion on !231 (closed), we have decided to package cern-magnum as two separate charts (one with only and another excluding the crds).

This is required as for when multiple dependencies with very large crds are enabled in cern-magnum installation breaks owning to us exceeding the 2MB secret limit for our helm release.

Hiding this change purley in the CI from a package / installation perspective provides the least intrusive approach (as it does not require restructuring or maintaining two `values.yaml` [one for crds and another for the umbrella chart], nor does it require complicated if gating around templates or crds). This is intended as a temporary solution until plans to migrate the management of cern-magnum as an applicationset in argo are planned for and completed later on in the year.