Re: Support logical replication of DDLs

Hi,

I added documentation and changed user interface design in the
attached v60 patch set.
The patch set addressed comments from Peter in [1].

The motivation for the user interface change is that we want to manage
DDL replication feature in stages with fine grained replication
levels.
For example, we can focus on reviewing and testing table commands
first, then other commands. It also make sense to introduce different
DDL replication levels
from the user perspective as pointed out in [1]. We can add more
replication levels along the way.

In this patch DDL replication is disabled by default and it can be
enabled at different levels
using the new PUBLICATION option 'ddl'. This option currently has two
levels and are
only allowed to be set if the PUBLICATION is FOR ALL TABLES.

all: this option enables replication of all supported DDL commands.
table: this option enables replication of Table DDL commands which include:
-CREATE/ALTER/DROP TABLE
-CREATE TABLE AS

Example:
Create a new publication with all ddl replication enabled:
CREATE PUBLICATION pub1 FOR ALL TABLES with (ddl = 'all');

Enable table ddl replication for an existing Publication:
ALTER PUBLICATION pub2 SET (ddl = 'table');

Also I break down ddl_deparse.c into two patches:
1.v60-0002-Functions-to-deparse-Table-DDL-commands.patch
2.v60-0003-Support-DDL-deparse-of-the-rest-commands.patch

Regards,
Zane

[1] https://www.postgresql.org/message-id/CAAD30UKX%3DPbojrjU0webYy7Y9mz1HmDTM3dx_JJXpc%2BdXW-EQQ%40mail.gmail.com