docs: usermanual: add new chapter gb-ns2-maintenance

Depends-On: I5571001a127c933397a4bc26e85410288d50fc2f (osmo-gsm-manuals.git)
Change-Id: I951cc10d86de4f16d2226b34eda55202373c2524
diff --git a/doc/manuals/osmogbproxy-usermanual.adoc b/doc/manuals/osmogbproxy-usermanual.adoc
index c371cf7..2a1b873 100644
--- a/doc/manuals/osmogbproxy-usermanual.adoc
+++ b/doc/manuals/osmogbproxy-usermanual.adoc
@@ -29,6 +29,7 @@
 
 include::./common/chapters/gb-ns2-configuration-timer.adoc[]
 
+include::./common/chapters/gb-ns2-maintenance.adoc[]
 
 include::./common/chapters/control_if.adoc[]