samples: Bluetooth: Update unicast audio samples to use bidirectional

Modified the samples such that the client will attempt to
setup 2 sink streams and 1 source stream, basically
representing a headset use case.

This also excercises both setting up a unidirectional
and a bidirectional ISO channel using the 3 audio streams.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>