Switch to specialized Sentry PostgreSQL and wal2json Docker image

Summary:
Sentry requires a custom version of the extension wal2json
for the Change Data Capture (CDC) toolkit.

The Docker installer of Sentry hosted environment uses the Docker library
image, runs a container to get the curl command, then copies the file first
to the data volume, then to the expected PostgreSQL lib directory. Ouf!

Instead, this change uses a small image with wal2json.so directly saved
in the right expected PostgreSQL lib directory. This is provided by the
nasqueron/postgres-sentry image on Docker Hub, rDPGSENTRY here.

Ref T1791

Test Plan: Deploy on docker-002

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1791

Differential Revision: https://devcentral.nasqueron.org/D2865