le_audio: Move audio set configurations to json file

This replaces the existing audio set configuration provider
which serves proper target set configurations from the hard-coded
set of configurations.

Configurations are now beeing loaded from the external sources (json
files) using flatbuffers library. While schemas are loaded
from the precompiled binaries, configurations are all plain text
files loaded at run time. This allows for changing configs without
the build system being involved.

Bug: 150670922
Tag: #feature
Sponsor: jpawlowski@
Test: atest --host bluetooth_le_audio_test
Change-Id: I87e7e715000082170a9e7f61d79d039df62573b1