Improve resource naming for sessions and workspaces

[lucas-koehler]

Follow up of #326

Naming for resources that derive their name based on sessions and workspaces was already improved.
However, names for the session and workspaces objects themselves can still be improved.
The reason is that the original PR only improves naming in the operator. However, session and workspaces objects are created by the REST service.

Thus, the REST service should be adapted to create names similar to the operator.