Add worker type to pg_stat_subscription.

Thanks to commit 2a8b40e368, the logical replication worker type is
easily determined.  The worker type could already be deduced via
other columns such as leader_pid and relid, but that is unnecessary
complexity for users.

Bumps catversion.

Author: Peter Smith
Reviewed-by: Michael Paquier, Maxim Orlov, Amit Kapila
Discussion: https://postgr.es/m/CAHut%2BPtmbSMfErSk0S7xxVdZJ9XVE3xVLhqBTmT91kf57BeKDQ%40mail.gmail.com

src/backend/catalog/system_views.sql

@@ -949,6 +949,7 @@ CREATE VIEW pg_stat_subscription AS
     SELECT
             su.oid AS subid,
             su.subname,
+            st.worker_type,
             st.pid,
             st.leader_pid,
             st.relid,

src/backend/replication/logical/launcher.c

@@ -1278,7 +1278,7 @@ GetLeaderApplyWorkerPid(pid_t pid)
 Datum
 pg_stat_get_subscription(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_SUBSCRIPTION_COLS	9
+#define PG_STAT_GET_SUBSCRIPTION_COLS	10
 	Oid			subid = PG_ARGISNULL(0) ? InvalidOid : PG_GETARG_OID(0);
 	int			i;
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
@@ -1339,6 +1339,22 @@ pg_stat_get_subscription(PG_FUNCTION_ARGS)
 		else
 			values[8] = TimestampTzGetDatum(worker.reply_time);
 
+		switch (worker.type)
+		{
+			case WORKERTYPE_APPLY:
+				values[9] = CStringGetTextDatum("apply");
+				break;
+			case WORKERTYPE_PARALLEL_APPLY:
+				values[9] = CStringGetTextDatum("parallel apply");
+				break;
+			case WORKERTYPE_TABLESYNC:
+				values[9] = CStringGetTextDatum("table synchronization");
+				break;
+			case WORKERTYPE_UNKNOWN:
+				/* Should never happen. */
+				elog(ERROR, "unknown worker type");
+		}
+
 		tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc,
 							 values, nulls);