docs(fileUpload): add validation example

examples/validation/core/27_file_upload.py

@@ -0,0 +1,23 @@
+from trame.app import get_server
+from trame.ui.vuetify import SinglePageWithDrawerLayout
+from trame.widgets import vuetify
+from trame.app.file_upload import ClientFile
+
+
+server = get_server()
+
+with SinglePageWithDrawerLayout(server) as layout:
+    with layout.toolbar:
+        vuetify.VFileInput(
+            v_model=("file_exchange", None),
+        )
+
+
+@server.state.change("file_exchange")
+def handle(file_exchange, **kwargs):
+    file = ClientFile(file_exchange)
+    print(file.info)
+
+
+if __name__ == "__main__":
+    server.start()