Use appropriate icon for unconfigured applets' "Configure..." buttons

Summary: CCBUG: 412114

Test Plan:
{F8116018}

(The icon size is too large by default but that's not a bug in this patch)

Reviewers: #plasma, davidedmundson, meven, ndavis

Reviewed By: meven, ndavis

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D27530

components/containmentlayoutmanager/qml/BasicAppletContainer.qml

@@ -136,6 +136,7 @@ ContainmentLayoutManager.AppletContainer {
     configurationRequiredComponent: PlasmaComponents.Button {
         anchors.centerIn: parent
         text: i18n("Configure...")
+        icon.name: "configure"
         visible: applet.configurationRequired
         onClicked: applet.action("configure").trigger();
     }