PXD-2731: Create Arborist client on client-create

[fantix]

This requires uc-cdis/arborist#53.

• [x] Should we add policies to client-modify?
• [x] What about existing clients? Should sync also sync clients?

[PlanXCyborg]

The style in this PR agrees with black. :heavy_check_mark:

This formatting comment was generated automatically by a script in uc-cdis/wool.

[Avantol13]

I think we should handle clients during syncing.. if we are specifying user policies in the user.yaml we should be able to specify client policies as well. It would be sorta strange to only support some of the arborist features in the user.yaml and require fence-create calls for modifying others. I like this as a bootstrapping/initial creation feature, but ideally I think the sync needs to handle assigning policies to existing clients so that you dont have to go back and run fence-create if things change

[fantix]

Created PXD-3064 for managing client policies in user.yaml.