Fix unqualified catalog references in psql describe queries

Hi,

While testing "[aecc55866] psql: Show comments in \dRp+, \dRs+, and \dX+", I noticed a small issue that was actually introduced by "[8185bb534] CREATE SUBSCRIPTION … SERVER”.

The problem is that, when querying pg_foreign_server, it misses the "pg_catalog" schema qualification:
```
appendPQExpBuffer(&buf,
", (select srvname from pg_foreign_server where oid=subserver) AS \"%s\"\n",
gettext_noop("Server"));
```

This is not a big problem, but it provides a way to pollute the result of \dRs+ by adding a fake pg_foreign_server earlier in search_path. See this repro:

1. Setup: create a server and a sub
```
evantest=# create extension postgres_fdw;
CREATE EXTENSION
evantest=# create publication pub;
CREATE PUBLICATION
evantest=# create server s foreign data wrapper postgres_fdw options (dbname 'postgres');
CREATE SERVER
evantest=# create user mapping for current_user server s;
CREATE USER MAPPING
evantest=# create subscription sub server s publication pub with (connect=false, slot_name=none);
WARNING: subscription was created, but is not connected
HINT: To initiate replication, you must manually create the replication slot, enable the subscription, and alter the subscription to refresh publications.
CREATE SUBSCRIPTION
evantest=# \dRs+ sub;
List of subscriptions
Name | Owner | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Server | Retain dead tuples | Max retention duration | Retention active | Synchronous commit | Conninfo | Receiver timeout | Skip LSN | Description
------+-------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------+--------------------+------------------------+------------------+--------------------+----------+------------------+------------+-------------
sub | chaol | f | {pub} | f | parallel | d | f | any | t | f | f | s | f | 0 | f | off | | -1 | 0/00000000 |
(1 row)
```

As shown above, “Server” column shows the correct server name “s”.

2. Now, pollute the result
```
evantest=# create temp table pg_foreign_server (oid oid, srvname name);
CREATE TABLE
evantest=# insert into pg_foreign_server select oid, 'fake_s'::name from pg_catalog.pg_foreign_server where srvname='s';
INSERT 0 1
evantest=# \dRs+ sub;
List of subscriptions
Name | Owner | Enabled | Publication | Binary | Streaming | Two-phase commit | Disable on error | Origin | Password required | Run as owner? | Failover | Server | Retain dead tuples | Max retention duration | Retention active | Synchronous commit | Conninfo | Receiver timeout | Skip LSN | Description
------+-------+---------+-------------+--------+-----------+------------------+------------------+--------+-------------------+---------------+----------+--------+--------------------+------------------------+------------------+--------------------+----------+------------------+------------+-------------
sub | chaol | f | {pub} | f | parallel | d | f | any | t | f | f | fake_s | f | 0 | f | off | | -1 | 0/00000000 |
(1 row)
```

Now, the "Server" column shows the fake server name that I supplied.

The fix is to add the schema qualification, using "pg_catalog.pg_foreign_server". In describe.c, catalog objects are generally referenced by qualified names. I found 3 other occurrences that missed schema qualification, so I fixed them as well.

There are 4 spots in total. Two are v19-new, oversights of 8185bb53476378443240d57f7d844347d5fae1bf and 2f094e7ac691abc9d2fe0f4dcf0feac4a6ce1d9c. The other two are older and might be worth back-patching. So I split the fix into 2 commits: 0001 is v19-new, and 0002 is a back-patch candidate.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/