Im sharing this document that i made hoping to help anyone , in case someone faces a requirment same as i did ,
it shows how to add users to specific permissions in workspace (admin , workflow , smo) Permissions .
since i couldnt find a way to interact with workspace directly , i created groups and these groups are added to workspace permissions ,
then my smartforms handles adding chosen users to the chosen permission .
Note : this approach could be applied if you are able to CREATE new domain groups and giving a specific USER full control into these groups (This specific user is going to be the one that uses the smartform to add users to permissions groups) , also these steps could apply for deleting users from permissions groups as well if you want to extend this form useage more and more .
Hope it helps!