fix: bootstrap build

[mayeut]

This PR declares a custom build backend for the CMake PyPI distrbution. The following are included:

• removes the Ninja PyPI distribution build dependency by default in order to break a build cycle (cmake -> ninja -> cmake) when binary wheels are not available and Ninja is not present/too old on the build system. (this is fix: do not require Ninja #566)
• removes the CMake PyPI distrbution build dependency by default in order to break a build cycle (cmake -> cmake) when binary wheels are not available and CMake is not present/too old on the build system.
• Uses a bootstrapped CMake in order to build itself when CMake is not present/too old on the build system.

Relates to #503 (comment).

The bootstrap build might not be efficient as we're building CMake twice but that's the easiest way I could think of and hopefully, those kind of builds should not happen that often.

close #566

[henryiii]

Okay to try it on the current release.