As part of ensuring all internal clients and operations are cluster-role-aware, they can be tagged with the Service (corresponding to a ClusterRole) they are running under. In this ticket, migrate ThreadClients that are being created with a raw ServiceContext to being created via a Service that they are a member of.

For now, just use the "default service" on the ServiceContext, which will be either Router or Shard depending on the binary. After this ticket, we will need to tag them specifically as the use of a "default service" is eliminated.