Bump cmake minimum version to 3.23

[m-kuhn]

This allows us to use FILE_SETs to avoid installing header files in some scenarios (e.g. mac packages).
There are other options as well, but I wonder if this requirement would be acceptable.

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[jef-n]

Breaks builds on jammy which has 3.22.1

[Alex-Kent]

As jef-n noted increasing the minimum CMake version for 3.23.0 breaks builds on Ubuntu 22.04 LTS Jammy which has 3.22.1. In practice the current QGIS master branch from Git builds fine if the minimum required CMake version is manually changed to 3.22.0. In other words, FILE_SET or other later features might be present in the CMakeFiles but those features don't appear to be used on the code path used for Ubuntu builds. In particular, the FILE_SET feature (the stated reason for increasing the required CMake version) doesn't appear to be used anywhere in the CMake files.

I suggest reverting this back to its previous value. If and when a CMake feature is needed that is only available via newer CMake versions then the minimum required version can be increased. Until that time the required CMake version should remain at the lower number. In other words, the requirement should match what is actually required to build QGIS using CMake, not the version needed for features that might be nice to use in future.