MM-12849 Moving all non request scoped items to Server struct (#9806)

* Moving goroutine pool

* Auto refactor

* Moving plugins.

* Auto refactor

* Moving fields to server

* Auto refactor

* Removing siteurl duplication.

* Moving reset of app fields

* Auto refactor

* Formatting

* Moving niling of Server to after last use

* Fixing unit tests.

app/websocket_router.go

@@ -55,7 +55,7 @@ func (wr *WebSocketRouter) ServeWebSocket(conn *WebConn, r *model.WebSocketReque
 			return
 		}
 
-		wr.app.Go(func() {
+		wr.app.Srv.Go(func() {
 			wr.app.SetStatusOnline(session.UserId, false)
 			wr.app.UpdateLastActivityAtIfNeeded(*session)
 		})