Add button for activating modes manually

Fixes: 308819907
Flag: android.app.modes_ui
Test: ZenModeButtonPreferenceControllerTest
Test: atest com.android.settings.notification.modes
Change-Id: Id018d360c648dd948d2f950ca67cfbea71cc5c68

src/com/android/settings/notification/modes/ZenModeHeaderController.java

@@ -51,6 +51,7 @@ class ZenModeHeaderController extends AbstractZenModePreferenceController {
         if (mFragment == null) {
             return;
         }
+        preference.setSelectable(false);
 
         if (mHeaderController == null) {
             final LayoutPreference pref = (LayoutPreference) preference;