fix(server): schema-qualify remaining pg_catalog calls in ServerNode

The SQL injection fix for create_restore_point now calls
pg_catalog.pg_create_restore_point so that a non-default search_path
on the connection cannot redirect the call to a shadow definition.
Apply the same hardening to the other pg_* calls in the same file
that were still unqualified: pg_reload_conf in reload_configuration,
and pg_xlog_replay_pause / pg_wal_replay_pause / pg_xlog_replay_resume
/ pg_wal_replay_resume in wal_replay.

These were not exploitable on their own -- the SQL string is static
and not user-derived -- but resolving them via pg_catalog removes any
dependency on the connection's search_path being trustworthy.