Generating default settings on PC and flashing them during provisioning

[TjazVracko]

Context

Default settings values could be provisioned at factory time.
A project exists (here), which is able to generate a .hex file containing a valid NVS image with settings. It supports string values only, but should be easily extendible to provision whatever.

The program should be run using the json representation of the user settings, as described in #4.

Required steps / Implementation details

TODO: figure out the exact steps

Definition of Done

I can run a program like ./prov_settings_gen -i settings.json which generates a settings.hex file.
The file can then be flashed onto the target (figure out exactly how to do this).
When the firmware is flashed and run, default values for the settings will be already set.