DOC: promex: Add missing backend metrics

"haproxy_backend_agg_server_status" and "haproxy_backend_agg_check_status"
were not referenced in promex README.

"haproxy_backend_agg_server_check_status" is also missing but it is a
deprecated metric. Thus, it is better to not reference it.

(cherry picked from commit 7edec90c002740df26d13f8f780f5ccd762fb876)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit e41897cad6400ca2a9de6d63af4ee7363563ac16)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 02495c9e7d1514b0134048c00a556e3cd6307a53)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit d2eb543ab5a3e6cad5b1fc1870c87ec41e80727c)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/addons/promex/README b/addons/promex/README
index e41ebdc..4e29e23 100644
--- a/addons/promex/README
+++ b/addons/promex/README
@@ -286,6 +286,8 @@
 | haproxy_backend_max_total_time_seconds              |
 | haproxy_backend_internal_errors_total               |
 | haproxy_backend_uweight                             |
+| haproxy_backend_agg_server_status                   |
+| haproxy_backend_agg_check_status                    |
 +-----------------------------------------------------+
 
 * Server metrics