bluetooth: dis: add Kconfig for disabling optional characteristics

Added new Kconfig option set that allows the user to control the
presence of the following optional characteristics:

- Manufacturer Name String
- Model Number String

Depreacted the old configuration that can be deleted in the future
Zephyr releases.

Signed-off-by: Kamil Piszczek <Kamil.Piszczek@nordicsemi.no>