Move all Kconfig symbols related to Bluetooth logging into the newly
created `Kconfig.logging`. The logging symbols are now grouped by into a
menu "Bluetooth logging". Closely related symbols are grouped with each
others. For example, audio related logging symbol are found behind a
submenu "Audio" inside the "Bluetooth logging".
The deprecated logging symbols have also been moved in a submenu of
"Bluetooth logging", it's easier to avoid them so.
Behavior of the Bluetooth logging system:
When `LOG` symbol is selected, if Bluetooth is enabled (`BT` symbol
selected), the Bluetooth logging is enabled.
If the user does not set any log level, the Bluetooth logging symbols
will inherit the log level of `BT_LOG_LEVEL`. If the user does not set
the level of `BT_LOG_LEVEL`, the default log level will be the one
defined by the logging subsystem. Which currently is `LOG_LEVEL_INF`.
Signed-off-by: Théo Battrel <theo.battrel@nordicsemi.no>
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