add wal2json extension

[olirice]

What kind of change does this PR introduce?

Adds the wal2json extension to the docker and ansible builds.

Purpose

Adding a logical decoding output plugin is a prerequisite to moving logical decoding from realtime to the postgres server and for developing an RLS strategy on the output stream.

Stability

The extension is 7 years old, actively maintained, 700+ GH stars and preinstalled on:

• RDS: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_PostgreSQL.html
• Azure: https://docs.microsoft.com/en-us/azure/postgresql/concepts-logical
• Digital Ocean: https://docs.digitalocean.com/products/databases/postgresql/resources/supported-extensions/

Compatibility

Install targets exist for postgres 9.5, 9.6, 10, 11, 12, and 13.

Example Output

select pg_create_logical_replication_slot('slot1', 'wal2json') create table account(id int primary key); insert into account(id) values (1); select * from pg_logical_slot_get_changes('slot1', null, null)

{ "change":[ { "kind":"insert", "schema":"public", "table":"account", "columnnames":[ "id" ], "columntypes":[ "integer" ], "columnvalues":[ 1 ] } ] }

[dragarcia]

lgtm! Merging it in.

[dragarcia]

Sidenote: I'll make sure this is part of the next release (13.3.0) (ref -#44)