Context:

Basically the same as for single reports. Once the combined report import has been added in the backend, we can add an import menu option for combined reports in the frontend as well.

API is the same as for other entities:
https://confluence.camunda.com/display/CO/Import#Import-ImportEntities 

AT:

• Combined reports can be imported via a menu item (only visible for superusers)
• import failures are communicated in the UI