Bluetooth: Add option to log btsnoops over RTT

There is a choice to log btmon logs over UART or RTT.
You can choose number of RTT buffer, set its name and size.

Replaced CONFIG_BT_DEBUG_MONITOR with CONFIG_BT_DEBUG_MONITOR_UART
for UART usage and CONFIG_BT_DEBUG_MONITOR_RTT for RTT.

Signed-off-by: Magdalena Kasenberg <magdalena.kasenberg@codecoup.pl>