Clean up the Signposter implementation and align on new metrics

ElementX/Sources/FlowCoordinators/RoomFlowCoordinator.swift

@@ -111,8 +111,6 @@ class RoomFlowCoordinator: FlowCoordinatorProtocol {
         self.flowParameters = flowParameters
         
         setupStateMachine()
-        
-        flowParameters.analytics.signpost.beginRoomFlow(roomID)
     }
         
     // MARK: - FlowCoordinatorProtocol
@@ -129,6 +127,7 @@ class RoomFlowCoordinator: FlowCoordinatorProtocol {
         
         switch appRoute {
         case .room(let roomID, let via):
+            flowParameters.analytics.signpost.startTransaction(.openRoom)
             Task {
                 await handleRoomRoute(roomID: roomID, via: via, animated: animated)
             }
@@ -897,7 +896,6 @@ class RoomFlowCoordinator: FlowCoordinatorProtocol {
         } else {
             actionsSubject.send(.finished)
         }
-        flowParameters.analytics.signpost.endRoomFlow()
     }
     
     private func presentRoomDetails(isRoot: Bool, animated: Bool) async {