Adding resource roles to allowed assignments
Adding resource roles to allowed assignments

Adding resource_admin and resource_viewer to the allowed roles, which can be assigned in elektra. 
viewer might be relevant for user not having the member role.
This is a followup for https://github.com/sapcc/elektra/commit/0b47950cbfa2180d1d635fc9e9271a1f00236b99

//cc @urfuwo @majewsky @Carthaca
sapcc/elektra,sapcc/elektra,sapcc/elektra,sapcc/elektra