Support fetching charts from dev.gitlab.org internal registry
As part of security release, the charts will be first pushed to the Helm registry of dev.gitlab.org (done via gitlab-org/charts/gitlab!2171 (merged)). We should update the add_gitlab_repo.sh and retrieve_gitlab_charts.sh scripts to pull from dev registry while on a dev.gitlab.org pipeline.
This is required before we can implement #224 (closed)