pgsql: Add pg_get_database_ddl() function

Add pg_get_database_ddl() function

Add a new SQL-callable function that returns the DDL statements needed
to recreate a database. It takes a regdatabase argument and an optional
VARIADIC text argument for options that are specified as alternating
name/value pairs. The following options are supported: pretty (boolean)
for formatted output, owner (boolean) to include OWNER and tablespace
(boolean) to include TABLESPACE. The return is one or multiple rows
where the first row is a CREATE DATABASE statement and subsequent rows are
ALTER DATABASE statements to set some database properties.

The caller must have CONNECT privilege on the target database.

Author: Akshay Joshi <akshay(dot)joshi(at)enterprisedb(dot)com>
Co-authored-by: Andrew Dunstan <andrew(at)dunslane(dot)net>
Co-authored-by: Euler Taveira <euler(at)eulerto(dot)com>
Reviewed-by: Japin Li <japinli(at)hotmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Álvaro Herrera <alvherre(at)kurilemu(dot)de>
Reviewed-by: Quan Zongliang <quanzongliang(at)yeah(dot)net>
Discussion: https://postgr.es/m/CANxoLDc6FHBYJvcgOnZyS+jF0NUo3Lq_83-rttBuJgs9id_UDg@mail.gmail.com
Discussion: https://postgr.es/m/e247c261-e3fb-4810-81e0-a65893170e94@dunslane.net

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a4f774cf1c7e5c6cf2f3393f611e1df16cdb5a5a

Modified Files
--------------
doc/src/sgml/func/func-info.sgml | 23 ++
src/backend/utils/adt/ddlutils.c | 330 +++++++++++++++++++++++++++++
src/include/catalog/pg_proc.dat | 8 +
src/test/regress/expected/database_ddl.out | 88 ++++++++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/database_ddl.sql | 66 ++++++
6 files changed, 516 insertions(+), 1 deletion(-)