Disable huge pages in postgres

With the default setting (try), postgres tries to use mmap, which is not
allowed inside the snap.

src/postgres/config/postgresql.conf

@@ -1,6 +1,7 @@
 max_connections = 100
 shared_buffers = 128MB
 ssl = off
+huge_pages = off
 external_pid_file = '$PID_DIR/postgres.pid'
 log_destination = 'stderr'
 logging_collector = off