Upgrade ubuntu image to 24.04 (LTS) and ffmpeg to 7.1

[jsheffie]

per this pr comment: https://github.com/jrottenberg/ffmpeg/pull/408#issuecomment-2394907208 this Issue is now

2404 is the current TLS, https://endoflife.date/ubuntu

• Update Ubuntu to 24.04 and ffmpeg to 7.1

Initial issue was written as: Docker base template Dockerfile-template.ubuntu2204 is pointing at an old base

Docker template `Dockerfile-template.ubuntu2204` is pointed at

FROM ubuntu:20.04 AS base

Which is old (March 2023), and misleading, since the template name specifies 2204.

should be FROM ubuntu:22.04 AS base

Ubuntu Release Reference 20.04/ 2023-03-22 14:31 - Ubuntu 20.04.6 LTS (Focal Fossa) 22.04/ 2024-09-12 18:47 - Ubuntu 22.04.5 LTS (Jammy Jellyfish)

For reference I found/realized because of a SOC2 Vulnerabilities Scan on the docker image.