CMake: Update minimum version to 3.22.1

[M2-TE]

Updated to match Vulkan-Headers, Vulkan Validation Layers and SPIR-V Tools.
See KhronosGroup/Vulkan-Headers#525

Removed ci for ubuntu-20.04 as it only ships CMake 3.16.3

[asuessenbach]

I don't see why we should push the CMake minimum version to 3.22.1. We can live with what we have, can't we?

[M2-TE]

The plan was to add Vulkan-Headers via add_subdirectory or FetchContent instead of just adding the include directory, as we could make use of their version check and also prevent the currently duplicated header files (vulkan.hpp is present in both Vulkan-Headers and Vulkan-Hpp), while also providing the Vulkan::Headers target, if people need it.

These things are not strictly necessary, but I figured it would make sense to update to the same version as the Vulkan-Headers dependency, which would also enable some extra aforementioned things. A version range via 3.12...3.22.1 might also do the trick to not place any hard requirements.

If you think it's not needed, feel free to just close this PR!

[asuessenbach]

In fact, I don't think, it's needed.
And what's more important here: I don't like to cut down the CI by removing the checks on Ubuntu 20.04, just to keep CMake happy.
That is: as long as there's no substantial reason to require a newer version of CMake I'd like to stay with it.