Add warning while creating keytab entry

In creating keytab entry during the configuration of direct AD
integration with GSS-Proxy, we can warn the end-user about connectivity
between hosts and domain. This will save the time for end-users.

https://bugzilla.redhat.com/show_bug.cgi?id=2159686
(cherry picked from commit 018cb2e)

guides/common/modules/proc_configuring-direct-ad-integration-with-gss-proxy.adoc

@@ -53,6 +53,8 @@ euid = __ID_of_Apache_User__
 ----
 . Create a keytab entry:
 +
+WARNING: The host must not be enrolled to a domain before creating a keytab entry.
++
 [options="nowrap", subs="+quotes,verbatim,attributes"]
 ----
 # KRB5_KTNAME=FILE:/etc/httpd/conf/http.keytab net ads keytab add HTTP -U administrator -d3 -s /etc/net-keytab.conf