doc: releases: document the DIS changes in changelog and migration guide

Added a changelog entry in the Deprecated and New categories to document
the Kconfig changes for the Bluetooth Device Information Service (DIS).
Updated the migration guide to provide instructions on how to
transition from the old configuration scheme to the new one.

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