Update ubuntu version from 18.04 to 22.04

[eugeneteoh]

Context

Ubuntu 18.04 has reached end of life.

Suggested solution

Ubuntu images should be upgraded to the latest LTS version, 22.04.

Considered alternatives

Additional details

Vulkan doesn't work out of the box in ubuntu:18.04 image.

$ vulkaninfo
===========
VULKAN INFO
===========

Vulkan Instance Version: 1.1.70

/build/vulkan-UL09PJ/vulkan-1.1.70+dfsg1/demos/vulkaninfo.c:2700: failed with VK_ERROR_INITIALIZATION_FAILED

[webbertakken]

I agree, it's time.

We're gonna need to sort out which dependencies are needed for 20.04 or 22.04. Ideally the latter, but also depending on what the requirements of Unity Editor are.

[eugeneteoh]

Latter is good. Anything I can help with (e.g. which dependencies to look into)? I need it for my CI and I'd rather not have a custom image.

[webbertakken]

Sure.

First of all, it's important to understand how to iterate quickly. You can build images locally by following instructions in DEVELOPMENT.md

1. We'll need an upgrade of the base image, so that it's based on 22.04.
2. After that, the hub and editor images can be created. They will have to pass the build process.
3. Finally we'll need to ask a few people to test their use cases based on the changes from the PR. For example it'll need to work with all targetPlatforms as well as with ECS and burst compilation and the default projects with the different render pipelines should run without a hitch as well.

If any good changes were made that are also useful for other platforms:

• We'll need to repeat the same steps for Windows.
• MacOS does not yet have images as per HostProcess containers for macOS containerd/containerd#5525

Once done, we'd have to do a major version bump for the images, so that old installations don't automatically start failing.