fixed #10540 - greatly improved `Donate CPU` section in documentation / cleaned up some donate-cpu scripts

[firewave]

The suggested script now is based on git so we will always run the latest version. It also makes sure the Python dependencies are always up-to-date.

[firewave]

@feelamee as you currently contributed to the section please have a look

[firewave]

This essentially fixes https://trac.cppcheck.net/ticket/10540.

[firewave]

I think I rather extract the script from the documentation and replace it with just add a wget and execution with a static link. We could also add an auto-update part to that script by limiting the amount of packages to analyze and then invoke the latest version again. That would greatly improve the user experience.

[firewave]

Will require some more reworking to make it better for causal users.