Add Plexus Mini support and project Kconfig for hardware targets

[JensOgorek]

Adds support for Plexus Mini (Plexus with different UART pins) and introduces project-level Kconfig to clearly select hardware targets and pins.

• New hardware targets: esp32_internal, plexus, plexus_mini (replaces esp32 and esp32s3)
• Kconfig: hardware choice and UART pin config
• Updated defaults: sdkconfig.defaults.esp32_internal, sdkconfig.defaults.plexus, sdkconfig.defaults.plexus_mini

How to build:

python3 build.py esp32_internal
python3 build.py plexus
python3 build.py plexus_mini

• Implement Plexus Mini support and Kconfig
• Add correct PINs for Plexus Mini to defaults
• Test with Plexus Mini
• Update & test workflow

[JensOgorek]

the release workflow will create this output :

• lizard_firmware_and_devtools_v0.x.0_esp32_internal.zip
• lizard_firmware_and_devtools_v0.x.0_plexus.zip
• lizard_firmware_and_devtools_v0.x.0_plexus_mini.zip
• lizard_v0.x.0_esp32_internal.bin
• lizard_v0.x.0_plexus.bin
• lizard_v0.x.0_plexus_mini.bin
• Source code (zip)
• Source code (tar.gz)

The naming for the binaries is slightly different for the direct binary only download, but still "lizard.bin" in the firmware and devtools.