node service: enable provision of the -S/--superuser option

This is required to be able to execute a CHECKPOINT if the normal
repmgr user is not a superuser.

doc/repmgr-node-service.xml

@@ -75,8 +75,22 @@
           <para>
             Issue a <command>CHECKPOINT</command> before stopping or restarting the node.
           </para>
+          <para>
+            Note that a superuser connection is required to be able to execute the
+             <command>CHECKPOINT</command> command.
+          </para>
         </listitem>
      </varlistentry>
+
+     <varlistentry>
+        <term><option>-S</option>/<option>--superuser</option></term>
+        <listitem>
+          <para>
+           Connect as the named superuser instead of the normal &repmgr; user.
+          </para>
+        </listitem>
+     </varlistentry>
+
     </variablelist>
 
   </refsect1>

repmgr-action-node.c

@@ -2028,10 +2028,44 @@ do_node_service(void)
 	{
 		PGconn	   *conn = NULL;
 
-		if (strlen(config_file_options.conninfo))
-			conn = establish_db_connection(config_file_options.conninfo, true);
+		if (config_file_options.conninfo[0] != '\0')
+		{
+			t_conninfo_param_list node_conninfo = T_CONNINFO_PARAM_LIST_INITIALIZER;
+			char	   *errmsg = NULL;
+			bool		parse_success = false;
+
+			initialize_conninfo_params(&node_conninfo, false);
+
+			parse_success = parse_conninfo_string(config_file_options.conninfo,
+												  &node_conninfo,
+												  &errmsg, false);
+
+			if (parse_success == false)
+			{
+				log_error(_("unable to parse conninfo string \"%s\" for local node"),
+						  config_file_options.conninfo);
+				log_detail("%s", errmsg);
+
+				exit(ERR_BAD_CONFIG);
+			}
+
+			/*
+			 * If --superuser option provided, attempt to connect as the specified user
+			 */
+
+			if (runtime_options.superuser[0] != '\0')
+			{
+				param_set(&node_conninfo,
+						  "user",
+						  runtime_options.superuser);
+			}
+
+			conn = establish_db_connection_by_params(&node_conninfo, true);
+		}
 		else
+		{
 			conn = establish_db_connection_by_params(&source_conninfo, true);
+		}
 
 		if (is_superuser_connection(conn, NULL) == false)
 		{

repmgr-client.c

@@ -1692,6 +1692,7 @@ check_cli_parameters(const int action)
 		{
 			case STANDBY_CLONE:
 			case NODE_CHECK:
+			case NODE_SERVICE:
 				break;
 			default:
 				item_list_append_format(&cli_warnings,