Generate translator comments for GUC parameter descriptions

Generate translator comments for GUC parameter descriptions

Automatically generate comments like

    /* translator: GUC parameter "client_min_messages" short description */

in the generated guc_tables.inc.c.

This provides translators more context.

Reviewed-by: Pavlo Golub <pavlo.golub@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Stéphane Schildknecht <sas.postgresql@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/1a89b3f0-e588-41ef-b712-aba766143cad%40eisentraut.org