Add the database name to the ps display of logical WAL senders

Logical WAL senders display now as follows, gaining a database name:
postgres: walsender USER DATABASE HOST(PORT) STATE

Physical WAL senders show up the same, as of:
postgres: walsender USER HOST(PORT) STATE

This information was missing, hence it was not possible to know from ps
if a WAL sender was a logical or a physical one, and on which database
it is connected when it is logical.

Author: Tatsuhiro Nakamori
Reviewed-by: Fujii Masao, Bharath Rupireddy
Discussion: https://postgr.es/m/36a3b137e82e0ea9fe7e4234f03b64a1@oss.nttdata.com

src/backend/postmaster/postmaster.c

@@ -4365,7 +4365,7 @@ BackendInitialize(Port *port)
 	if (am_walsender)
 		appendStringInfo(&ps_data, "%s ", GetBackendTypeDesc(B_WAL_SENDER));
 	appendStringInfo(&ps_data, "%s ", port->user_name);
-	if (!am_walsender)
+	if (port->database_name[0] != '\0')
 		appendStringInfo(&ps_data, "%s ", port->database_name);
 	appendStringInfoString(&ps_data, port->remote_host);
 	if (port->remote_port[0] != '\0')