[gnome-builder/wip/gtk4-port] plugins/buildui: add custom command button

[Christian Hergert <chergert src gnome org>]

commit 3b6144a371a80c7740232290de8b1ef75c72c7f6
Author: Christian Hergert <chergert redhat com>
Date:   Mon May 23 16:12:20 2022 -0700

    plugins/buildui: add custom command button
    
    So we don't forget to wire this up later.

 src/plugins/buildui/gbp-buildui-runnables-dialog.ui | 9 +++++++++
 1 file changed, 9 insertions(+)
---
diff --git a/src/plugins/buildui/gbp-buildui-runnables-dialog.ui 
b/src/plugins/buildui/gbp-buildui-runnables-dialog.ui
index d5906c0c3..34932dfdc 100644
--- a/src/plugins/buildui/gbp-buildui-runnables-dialog.ui
+++ b/src/plugins/buildui/gbp-buildui-runnables-dialog.ui
@@ -38,6 +38,15 @@
                     </child>
                   </object>
                 </child>
+                <child>
+                  <object class="GtkButton">
+                    <property name="margin-top">12</property>
+                    <property name="margin-bottom">12</property>
+                    <property name="use-underline">true</property>
+                    <property name="label" translatable="yes">_Custom Command…</property>
+                    <property name="halign">end</property>
+                  </object>
+                </child>
                 <child>
                   <object class="GtkListBox" id="list_box">
                     <property name="margin-top">12</property>