Use Ubuntu 20.04 as base for images

[orangejulius]

We're currently pinned to Ubuntu 18.04, which is a nice stable base image, but maybe we should consider upgrading to Ubuntu 20.04?

[orangejulius]

This is something we're thinking of doing relatively soon. It doesn't have to happen right away, as Ubuntu 18 will be supported for quite some time, but having some newer versions of packages could be nice.

The Ubuntu 20 Docker image is a bit smaller (62MB vs 72MB), so that's a nice bonus too.

We'd want to make sure all the Pelias components work well on Ubuntu 20. Our Github Action unit tests are already running on Ubuntu 20 with one exception: the interpolation engine has differing test output on Ubuntu 18 and 20 due to changes in the version of sqlite3 used.

As long as there aren't any other issues I don't see a reason why this would be a tough upgrade.

[missinglink]

The new LTS 22.04 was actually just released a few weeks ago: https://ubuntu.com/blog/ubuntu-22-04-lts-released

I wonder if we just skip straight to that to save having to upgrade twice?

[orangejulius]

Yeah, good idea, let's just go to Ubuntu 22.04. I'll open a new PR for that base image, and just opened pelias/pelias#951 to track the rest of the work required.