Add opt-in demotion database safety gate

ocf/loxthelion/managed-container.d/applications/postgresql/native_peers.sh

@@ -54,6 +54,11 @@ mc_pg_demote_database_shadow()
     if [ "${rc}" -ne 0 ]; then
         ocf_log warn \
             "managed-containerd demote.database shadow unavailable rc=${rc}"
+
+        if [ "${MC_DEMOTE_DATABASE_GATE:-false}" = true ]; then
+            return 1
+        fi
+
         return 0
     fi
 
@@ -76,6 +81,10 @@ if (
     else
         ocf_log err \
             "managed-containerd demote.database shadow MISMATCH response=${response}"
+
+        if [ "${MC_DEMOTE_DATABASE_GATE:-false}" = true ]; then
+            return 1
+        fi
     fi
 
     return 0
@@ -153,7 +162,11 @@ mc_pg_native_demote()
         return "${OCF_ERR_GENERIC}"
     }
 
-    mc_pg_demote_database_shadow
+    if ! mc_pg_demote_database_shadow; then
+        ocf_exit_reason \
+            "managed-containerd demote.database gate rejected demotion"
+        return "${OCF_ERR_GENERIC}"
+    fi
 
     if [ "$(printf '%s' "${target_node}" | tr '[:upper:]' '[:lower:]')" = \
          "$(printf '%s' "${local_node}" | tr '[:upper:]' '[:lower:]')" ]; then