Adds "helm-toolkit.utils.merge" which is a replacement for the
upstream sprig "merge" function which didn't quite do what we
wanted, specifically it didn't merge slices, it just overrode
one with the other. This PS also updates existing callsites
of the sprig merge with "helm-toolkit.utils.merge".
Change-Id: I456349558d4cf941d1bcb07fc76d0688b0a10782