Change base image used for CI jobs

Currently used image - registry.gitlab.com/charts/alpine-helm - seems to be deprecated in favor of the new one, available as: registry.gitlab.com/gitlab-org/gitlab-build-images:gitlab-charts-build-base

Therefore let's update the configuration :)

It will also upgrade used Helm version from 2.9.0 to 2.14.2, which should resolve some of the pipeline failures on existing feature branches.