Create an internal CMake code style guideline and enforce it with cmake-format or other tooling

We have quite a bit of CMake code in the code base.
Most of the code follows a loose code style in qtbase, and deviates quite a bit in other leaf repos.

We sometimes get internal and external contributors who are not familiar with the de-facto style and require some help.

It would be beneficial to have an official code style that we can point to.
Even better if we can automatically enforce and rewrite it with a tool.