Removes sdkconfig.p* files, use a single sdkconfig.defaults.

This is now 'overlaid' with flow3r-specific options by idf_ext.py.

Contributor sign-offs: https://git.card10.badge.events.ccc.de/badge23/firmware/-/issues/5

As part of the history rewrite we removed all unused micropython
submodules, so we don't have to use their machinery anymore to only
update submodules that are in use by our port.

This moves badge hardware generation selection over from a header file
into ESP-IDF configuratbility.

The generaiton can now be selected by specifying `BADGE_GENERATION` or
`-g` when running the initial built.

In addition, each generation now gets its own sdkconfig.defaults file
(instead named sdkconfig.$generation) and the big autogeneration
sdkconfig file gets yeeted.

This refactors the build system to be more in line with the average
ESP-IDF project.

This means that:
  1. `idf.py` from the main directory now works
  2. Adding components, running menuconfig, etc. should now be trivial.
  3. We don't have to edit files in micropython/ports/esp32/....

Hopefully this is the first step to yeeting the micropython checkout
from source and just depending on a submodule instead.

This adds initial support for building on Nix(OS). It can be tested by
following the updated README.md. The result should be the ability to
build the firmware without having to download any other dependencies.