Switch back sslcompression to be a normal input field in libpq

Per buildfarm member crake, any servers including a postgres_fdw server
with this option set would fail to do a pg_upgrade properly as the
option got hidden in f9264d15 by becoming a debug option, making the
restore of the FDW server fail.

This changes back the option in libpq to be visible, but still inactive
to fix this upgrade issue.

Discussion: https://postgr.es/m/YEbq15JKJwIX+S6m@paquier.xyz

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -167,6 +167,7 @@ ALTER SERVER testserver1 OPTIONS (
 	sslcert 'value',
 	sslkey 'value',
 	sslrootcert 'value',
+	sslcompression 'value',
 	sslcrl 'value',
 	--requirepeer 'value',
 	krbsrvname 'value',
@@ -8945,7 +8946,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcert, sslkey, sslrootcert, sslcrl, sslcrldir, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size, batch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, sslcrldir, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size, batch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -181,6 +181,7 @@ ALTER SERVER testserver1 OPTIONS (
 	sslcert 'value',
 	sslkey 'value',
 	sslrootcert 'value',
+	sslcompression 'value',
 	sslcrl 'value',
 	--requirepeer 'value',
 	krbsrvname 'value',

src/interfaces/libpq/fe-connect.c

@@ -298,7 +298,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 	 * compatibility.
 	 */
 	{"sslcompression", NULL, NULL, NULL,
-	"SSL-Compression", "D", 1, -1},
+	"SSL-Compression", "", 1, -1},
 
 	{"sslcert", "PGSSLCERT", NULL, NULL,
 		"SSL-Client-Cert", "", 64,