panel/RRDCharts: enable scrolling for RRDCharts on touchscreens

quote from extjs docs (AbstractChart.js):

 If you do have a chart inside a scrollable view, even if it has no
 interactions, you have to set its touchAction config to the following:

 touchAction: {
     panX: true,
     panY: true
 }

 Otherwise, if a touch action started on a chart,
 a swipe will not scroll the view.

Since we have RRDCharts always in a scrollable view, and it does not seem to
hurt non-touchscreens, enable it by default so that users on touchscreens
can scroll it.

Reported by users in the forum:
https://forum.proxmox.com/threads/minor-but-annoying-ipad-swipe-bug.93686

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/panel/RRDChart.js

@@ -155,6 +155,11 @@ Ext.define('Proxmox.widget.RRDChart', {
 	},
     },
 
+    touchAction: {
+	panX: true,
+	panY: true,
+    },
+
     constructor: function(config) {
 	let me = this;