Build postgres:11+periods Docker image

[runejuhl]

Hi,

I'm not sure if you're interested, but thought I'd offer this anyway. This Dockerfile builds a periods Debian package from the current branch and drops it into a postgres:11 image along with an init script that creates the periods extension on container start.

This is neat if you want to play around with periods, simply run this to spin up an instance and get a psql shell:

docker build -t $USER/postgres-periods:latest .
docker run -ti --rm -d -p 5432:5432 $USER/postgres-periods:latest
psql -h localhost -p 5432 -U postgres -w postgres

I'd be glad to polish it a bit more and write a few lines for the README if you're interested.

[xocolatl]

Sure, I could be interested in this. Some checks are failing, though, and it would be nice if it handled all supported versions.