[TASK] Update to ubuntu 22.04

[SweBarre]

Description

• updated base image to Ubuntu 22.04, closes Update Ubuntu  #528
• removed the use of deprecated apt-key in docker-build.sh
• added mongodb repository to installed supported mongodb version (v3.6 according to this article)
• removed unused functions in docker-build.sh

How Has This Been Tested?

Builds and runs locally (amd64), don't have access to arm HW though
Tested with podman version 4.4.4, docker version 24.0.5-ce, build a61e2b4c9and is currently running my controller on kubernets v1.27.6+k3s1

Checklist:

Go over all the following points, and put an x in all the boxes that apply.
If you're unsure about any of these, don't hesitate to ask. We're here to help!

• My code follows the code style of this project. (CI will test it anyway and also needs approval)
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[arkste]

i've tested your changes, works great on amd64, but there's no mongo 3.6 arm version and therefore the build fails on arm 😞

[SweBarre]

Sorry... missed that.
It seems that the earliest version with arm64 packages is 4.1... doh
I close this PR as I've moved on to a two container setup, one with unifi-ctrl and one with mongodb