Autocompletion when setting the search_path

[fbdb]

As discussed here, there is no autocompletion when setting the search_path (SET search_path TO bar).

As suggested, the first autocompletion can easily be implemented by adding search_path TO here: https://github.com/dbcli/pgcli/blob/435cf7f2843c1a161ad63d72b75b91d1ccba8200/pgcli/packages/pgliterals/pgliterals.json#L230