[PATCH] Add pg_get_tablespace_ddl() function to reconstruct CREATE TABLESPACE statement

Hello!

I am submitting a patch as a part of a larger Retail DDL functions project
described by Andrew Dunstan here:
https://www.postgresql.org/message-id/945db7c5-be75-45bf-b55b-cb1e56f2e3e9%40dunslane.net

This patch creates a function pg_get_tablespace_ddl, designed to retrieve
the full DDL statement for a tablespace. Users can obtain the DDL by
providing the tablespace name, like so:

    SELECT pg_get_tablespace_ddl('regress_owner_tblsp');
                                           pg_get_tablespace_ddl

---------------------------------------------------------------------------------------------------
     CREATE TABLESPACE regress_owner_tblsp OWNER regress_user LOCATION ''
WITH (random_page_cost = 3);


This patch includes documentation, comments, and regression tests, all of
which pass successfully.

--
Best,

Manni Wood
EnterpriseDB