plonecli: Modernized, Pythonic setup towards Plone 7

[MrTango]

The plan is to have a buildoutless setup, using modern pythonic tools like UV, HATCHLING, MXDEV aso.
Also using the pyproject.toml instead of the bobtemplate.cfg to find the package root and store settings.

[MrTango]

Note to myself, talk to @ericof during the sprint, to keep things in sync.