plugins/runcommand: use Kirigami.Dialog

The "Add Command" dialog in the settings for the Run Command plugin
looks rather broken at the moment, as the size is not explicitly set and
the default value ends up much smaller than the contents. It uses
QQC2.Dialog, even though the plugin makes heavy use of Kirigami. Using
Kirigami.dialog here would solve the sizing issue, and generally lead to
a more consistent interface.

This change makes the plugin use Kirigami.Dialog instead of QQC2.

BUG: 487438

plugins/runcommand/kdeconnect_runcommand_config.qml

@@ -56,11 +56,12 @@ ListView {
         helpfulAction: view.action
     }
 
-    QQC2.Dialog {
+    Kirigami.Dialog {
         id: addDialog
         title: "Add command"
 
         standardButtons: QQC2.Dialog.Save | QQC2.Dialog.Cancel
+        padding: Kirigami.Units.largeSpacing
 
         Kirigami.FormLayout {
             QQC2.TextField {