Add busy area for sending request in endpoint

Needlework.Net/Views/EndpointView.axaml

@@ -308,6 +308,8 @@
 					
 		</StackPanel>
 		<Grid Grid.Row="1" Grid.Column="4">
+			<controls:BusyArea BusyText="Loading..."
+							   IsBusy="{Binding SelectedPathOperation.IsBusy}">
 				<TabControl>
 					<TabItem Header="Preview">
 						<avalonEdit:TextEditor
@@ -320,6 +322,7 @@
 							FontSize="12"/>
 					</TabItem>
 				</TabControl>
+			</controls:BusyArea>
 		</Grid>
 	</Grid>
 </UserControl>