Bluetooth: host: Add API for advertising sets

Add API for creating and starting advertising sets. This allows to start
and advertising set for a specific timeout or number of events.
The advertising set can be configured to advertise extended data on
secondary advertising channels or advertise on LE Coded PHY to give the
advertiser longer range.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>