magic: added a way for running async functions in the top level jsx code

shared/ssr.ts

@@ -1,6 +1,11 @@
+import { DatabaseConnection } from './database'
+
+export type ServerAsyncCallback = () => Promise<void>
+
 export type RenderedPage = {
     html: string
     metadata: any
+    asyncCallbacks: ServerAsyncCallback[]
 }
 
-export type RenderFunction = (url: string) => RenderedPage
+export type RenderFunction = (url: string, db: DatabaseConnection) => RenderedPage