fix: fix flake in TestWorkspaceAgentClientCoordinate_ResumeToken (#14642)

fixes #14365

I bet what's going on is that in `connectToCoordinatorAndFetchResumeToken()` we call `Coordinate()`, send a message on the `Coordinate` client and then close it in rapid succession. We don't wait around for a response from the coordinator, so dRPC is likely aborting the call `Coordinate()` in the backend because the stream is closed before it even gets a chance.

Instead of using the Coordinator to record the peer ID assigned on the API call, we can wrap the resume token provider, since we call that API _and_ wait for a response. This also affords the opportunity to directly assert we get called with the right token.

coderd/workspaceagents.go

@@ -864,6 +864,8 @@ func (api *API) workspaceAgentClientCoordinate(rw http.ResponseWriter, r *http.R
 			})
 			return
 		}
+		api.Logger.Debug(ctx, "accepted coordinate resume token for peer",
+			slog.F("peer_id", peerID.String()))
 	}
 
 	api.WebsocketWaitMutex.Lock()