cli: Make `rad id update` description optional
If a --title is specified, the description is optional, and will be
set to the empty string.
If a --title is specified, the description is optional, and will be
set to the empty string.
If a --title is specified, the description is optional, and will be
set to the empty string.
If a --title is specified, the description is optional, and will be
set to the empty string.