Update Dockerfile to Ubuntu 22.04

Since we no longer plan to actively support Ubuntu 20.04, we should update our [Dockerfile](https://github.com/firelab/windninja/blob/master/Dockerfile) to Ubuntu 22.04. We can use our [22.04 dependencies script](https://github.com/firelab/windninja/blob/master/scripts/build_deps_ubuntu_2204.sh) as a reference for what needs updated. 