Add test infrastructure for Charts on dev
Spinoff from https://gitlab.com/charts/gitlab/issues/1337
We need a way to test the Charts before they are actually released into the public. Right now, tagging and publishing of charts happen in one go. With https://gitlab.com/charts/gitlab/issues/1411 we will be splitting this to two, so release will be a manual job (played automatically by release-tools). This means, we get to add a test stage after tagging the Charts. https://gitlab.com/charts/gitlab/merge_requests/825 will be adding a wait-for-images logic to Charts, so this test stage can use the tagged CNG images from dev.
We need to create a cluster, hook it up to Charts repo in dev, alter the CI jobs to have the jobs run on dev too (at least tags).