updates Dockerfile; fixes ubuntu version: 20.04

[iper-jkane]

fix issue with docker build; version jammy (latest) was throwing errors.
Last known good version was 20.04, and it apparently still works.

also:
adds DEBIAN_FRONTEND=noninteractive env var
which means apt wont ask the user any questions.

[iper-jkane]

Hi,

as discussed with Lauren, Oriol, Arnau, et al;
this is a pull request to fix a deployment issue (I was experiencing) with the dockerized tools image / container.

Hopefully I haven't missed anything too obvious :)
but just let me know if you need more info, etc...