switchover: check for pending archive files on the demotion candidate

If the current primary (demotion candidate) still has any files to archive,
it will delay the shutdown until all files are archived. If there is a
substantial number of files, and/or the archive command executes slowly,
this will probably lead to an unwelcome delay in the switchover process.

configfile.h

@@ -72,6 +72,10 @@ typedef struct
 	char		restore_command[MAXLEN];
 	TablespaceList tablespace_mapping;
 
+	/* node check settings */
+	int			archiver_lag_warning;
+	int			archiver_lag_critical;
+
 	/* repmgrd settings */
 	failover_mode_opt		failover_mode;
 	char		location[MAXLEN];
@@ -124,6 +128,8 @@ typedef struct
 		"", "", "", DEFAULT_LOG_STATUS_INTERVAL,	\
 		/* standby clone settings */ \
 		false, "", "", "", "", { NULL, NULL },	\
+		/* node check settings */ \
+		DEFAULT_ARCHIVER_LAG_WARNING, DEFAULT_ARCHIVER_LAG_CRITICAL, \
 		/* repmgrd settings */ \
 		FAILOVER_MANUAL, DEFAULT_LOCATION, DEFAULT_PRIORITY, "", "", \
 		DEFAULT_MONITORING_INTERVAL, \