Bluetooth: CSIP: Add support for dynamically setting set size

The set size can now be dynamically set and notified.
The rank is added as a argument in the case that changing
the set size, also affects the device's rank, as ranks
in a coordinated set needs to be continuous.

The set coordinator implementation has been updated
to support receiving the new set size, and providing
this information to the upper layers.

This commit adds a babblesim test for the new API,
as well as a shell command.

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