BUG/MINOR: promex: create haproxy_backend_agg_server_status

haproxy_backend_agg_server_check_status currently aggregates
haproxy_server_status instead of haproxy_server_check_status.
We deprecate this and create a new one,
haproxy_backend_agg_server_status to clarify what it really
does.

This patch could be backported as far as 2.4.
diff --git a/addons/promex/service-prometheus.c b/addons/promex/service-prometheus.c
index b54695c..9330a86 100644
--- a/addons/promex/service-prometheus.c
+++ b/addons/promex/service-prometheus.c
@@ -302,6 +302,7 @@
 	[ST_F_NEED_CONN_EST]        = { .n = IST("need_connections_current"),         .type = PROMEX_MT_GAUGE,    .flags = (                                                                       PROMEX_FL_SRV_METRIC) },
 	[ST_F_UWEIGHT]              = { .n = IST("uweight"),                          .type = PROMEX_MT_GAUGE,    .flags = (                                               PROMEX_FL_BACK_METRIC | PROMEX_FL_SRV_METRIC) },
 	[ST_F_AGG_SRV_CHECK_STATUS] = { .n = IST("agg_server_check_status"),	      .type = PROMEX_MT_GAUGE,    .flags = (                                               PROMEX_FL_BACK_METRIC                       ) },
+	[ST_F_AGG_SRV_STATUS ]      = { .n = IST("agg_server_status"),	              .type = PROMEX_MT_GAUGE,    .flags = (                                               PROMEX_FL_BACK_METRIC                       ) },
 };
 
 /* Description of overridden stats fields */
@@ -833,7 +834,8 @@
 				return -1;
 
 			switch (ctx->field_num) {
-				case ST_F_AGG_SRV_CHECK_STATUS:
+				case ST_F_AGG_SRV_CHECK_STATUS: // DEPRECATED
+				case ST_F_AGG_SRV_STATUS:
 					if (!px->srv)
 						goto next_px;
 					sv = px->srv;
diff --git a/include/haproxy/stats-t.h b/include/haproxy/stats-t.h
index 1a7d3d1..a50676a 100644
--- a/include/haproxy/stats-t.h
+++ b/include/haproxy/stats-t.h
@@ -455,6 +455,7 @@
 	ST_F_USED_CONN_CUR,
 	ST_F_NEED_CONN_EST,
 	ST_F_UWEIGHT,
+	ST_F_AGG_SRV_STATUS,
 	ST_F_AGG_SRV_CHECK_STATUS,
 	ST_F_SRID,
 
diff --git a/src/stats.c b/src/stats.c
index 6ce4117..7d34e54 100644
--- a/src/stats.c
+++ b/src/stats.c
@@ -259,7 +259,8 @@
 	[ST_F_USED_CONN_CUR]                 = { .name = "used_conn_cur",               .desc = "Current number of connections in use"},
 	[ST_F_NEED_CONN_EST]                 = { .name = "need_conn_est",               .desc = "Estimated needed number of connections"},
 	[ST_F_UWEIGHT]                       = { .name = "uweight",                     .desc = "Server's user weight, or sum of active servers' user weights for a backend" },
-	[ST_F_AGG_SRV_CHECK_STATUS]          = { .name = "agg_server_check_status",     .desc = "Backend's aggregated gauge of servers' state check status" },
+	[ST_F_AGG_SRV_CHECK_STATUS]          = { .name = "agg_server_check_status",     .desc = "[DEPRECATED] Backend's aggregated gauge of servers' status" },
+	[ST_F_AGG_SRV_STATUS ]               = { .name = "agg_server_status",           .desc = "Backend's aggregated gauge of servers' status" },
 	[ST_F_SRID]                          = { .name = "srid",                        .desc = "Server id revision, to prevent server id reuse mixups" },
 };
 
@@ -2677,7 +2678,8 @@
 					chunk_appendf(out, " (%d/%d)", nbup, nbsrv);
 				metric = mkf_str(FO_STATUS, fld);
 				break;
-			case ST_F_AGG_SRV_CHECK_STATUS:
+			case ST_F_AGG_SRV_CHECK_STATUS:   // DEPRECATED
+			case ST_F_AGG_SRV_STATUS:
 				metric = mkf_u32(FN_GAUGE, 0);
 				break;
 			case ST_F_WEIGHT: