Dask Gateway: Migrate to HA Cluster and define a production-ready networking solution.

A PoC DG deployment has been used so far, but it should be migrated to the new HA cluster for more longevity (with the added benefit of spreading knowledge about the GitOps system through team). As part of this, we would also need to modify the networking. Currently to allow raw TCP traffic into the cluster we have used a separate proxy machine (accessed via floating IP); the routing should occur via the main proxy (either listening on a different port, or with a new domain associated).