Fix timeout handling in logical replication worker

The timestamp tracking the last moment a message is received in a
logical replication worker was initialized in each loop checking if a
message was received or not, causing wal_receiver_timeout to be ignored
in basically any logical replication deployments.  This also broke the
ping sent to the server when reaching half of wal_receiver_timeout.

This simply moves the initialization of the timestamp out of the apply
loop to the beginning of LogicalRepApplyLoop().

Reported-by: Jehan-Guillaume De Rorthais
Author: Julien Rouhaud
Discussion: https://postgr.es/m/CAOBaU_ZHESFcWva8jLjtZdCLspMj7vqaB2k++rjHLY897ZxbYw@mail.gmail.com
Backpatch-through: 10

src/backend/replication/logical/worker.c

@@ -1089,6 +1089,8 @@ UpdateWorkerStats(XLogRecPtr last_lsn, TimestampTz send_time, bool reply)
 static void
 LogicalRepApplyLoop(XLogRecPtr last_received)
 {
+	TimestampTz last_recv_timestamp = GetCurrentTimestamp();
+
 	/*
 	 * Init the ApplyMessageContext which we clean up after each replication
 	 * protocol message.
@@ -1107,7 +1109,6 @@ LogicalRepApplyLoop(XLogRecPtr last_received)
 		int			len;
 		char	   *buf = NULL;
 		bool		endofstream = false;
-		TimestampTz last_recv_timestamp = GetCurrentTimestamp();
 		bool		ping_sent = false;
 		long		wait_time;