Add setup for gitlab-elasticsearch-indexer
The new Go indexer will become the default with https://gitlab.com/gitlab-org/gitlab-ee/issues/6481 so we need to set it up in GDK.
Corresponding Rails changes are in https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/14728, these two MRs can be merged independently.
Ref: #338 (closed)
Edited by 🤖 GitLab Bot 🤖