Bluetooth: Audio: HAS: Fix notifications/indications

Before this commit we simply always notified/indicated
all presets and active index to any bonded device, even
if they never subscribed to anything, or even if we never
registered HAS.

This commit modifies that, so that only the proper
connected clients will get the notifications/indications,
and that we only send them if something has changed.

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