Add characteristics descriptor discovery option in gatttool
Add characteristics descriptor discovery option in gatttool

Only skeleton for new option was added (no callback).

pstglia/external-bluetooth-bluez,ComputeCycles/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez,ComputeCycles/bluez,silent-snowman/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez,ComputeCycles/bluez,pkarasev3/bluez,ComputeCycles/bluez,pkarasev3/bluez