KeystoneV3: Adding support for option field in Roles 

Added description field in previous PR. The role resource in keystone API also offers option as a field. Good idea to add support for this field as well in gophercloud.

reference: [click me](https://docs.openstack.org/api-ref/identity/v3/index.html#create-role:~:text=about%20the%20role.-,options%20(Optional),-body)
