Mark sslkeylogfile as Debug option

Mark the sslkeylogile option as "D" debug as this truly is a debug
option, and it will allow postgres_fdw et.al to filter it out as
well.  Also update the display length to match that for an ssl key
as they are both filename based inputs.

Author: Daniel Gustafsson <daniel@yesql.se>
Reported-by: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://postgr.es/m/CAOYmi+=5GyBKpu7bU4D_xkAnYJTj=rMzGaUvHO99-DpNG_YKcw@mail.gmail.com

src/interfaces/libpq/fe-connect.c

@@ -402,7 +402,7 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
 	offsetof(struct pg_conn, oauth_scope)},
 
 	{"sslkeylogfile", NULL, NULL, NULL,
-		"SSL-Key-Log-File", "", 0,	/* sizeof("") = 0 */
+		"SSL-Key-Log-File", "D", 64,
 	offsetof(struct pg_conn, sslkeylogfile)},
 
 	/* Terminating entry --- MUST BE LAST */