Use Testcontainers as default for testing

[DavideD]

Now that testcontainers seems to work well on all operating systems, I think we can use it as default.
We still need to be able to test on machines not started via docker/podman.

My proposal is to remove -Pdocker (it's going to be the default) and instead have something like -PskipContainers for when we don't want to use Testcontainers or docker. We need to rememeber to update the file podman.md

[DavideD]

I've decided I'm not going to use testcontainers (or docker) as default, because everytime I change or upgrade OS there are some problem with it.

I can start the container easily manually and that's the way I work most of the time anyway.

[DavideD]

I haven't had issues with Testcontainers in a long time, I think we can now enable it as default