[EPIC] Support attributing costs to individual hubs automatically on HHMI

[yuvipanda]

As part of #4384, we want to support attributing costs to individual hubs on GCP. This is the equivalent of #4453 but on GCP.

We don't want to do this on all hubs on all clusters, but need to pick a cluster that has multiple hubs already in it to attribute costs. Let's pick hhmi - it has a staging and prod hub, but also an ephemeral hub with binderhub UI.

While this EPIC is focused on hhmi, at the end of it, it would allow us to know exactly what we would need to do to do the same on any other cluster.