LeAudio: Minor configuration update cleanup and unit test

This cleans up the code and adjust function naming for better
readability. New unit test are also added.

Bug: 281686787
Bug: 285647765
Test: atest bluetooth_le_audio_test bluetooth_le_audio_client_test
Change-Id: I83d0f40f8c7ddd7314e795a41a7db9a3fa3eae0e