Add 16beta3 CI images

[naisila]

wal2json is needed for cdc tests, so we certainly can't merge like this. Last year wal2json support for pg15 was provided in July. Let's wait a bit before deciding on this.

However I am using this current PR to run the other PG16 tests in my branch of PG16 support PR

[hanefi]

Do the regression tests on Citus pass without wal2json packages?

[naisila]

@hanefi I forgot to convert this to draft PR. wal2json is needed for cdc tests, so we certainly can't merge like this. Last year wal2json support for pg15 was provided in July. Let's wait a bit before deciding on this.

However I am using this current PR to run the other PG16 tests in my branch.

[hanefi]

Nice solution. I have only one suggestion that can reduce docker layer cache sizes.

[hanefi]

An excerpt from Dockerfile best practices on apt-get section :

... when you clean up the apt cache by removing /var/lib/apt/lists it reduces the image size, since the apt cache isn’t stored in a layer. Since the RUN statement starts with apt-get update, the package cache is always refreshed prior to apt-get install.

I learned quite a lot from this piece of documentation about how docker works, and I recommend others to read that as well.

[hanefi]

all good except a small spacing issue