Issue Summary

Users that are not product admins and have the "Manage maintenances" permission are unable to schedule maintenances. Only product admins, or users with the "Manage incidents" page permission are able to do so. 

Steps to Reproduce

1. Have an account with access to a page and the "Manage maintenances" permission, but not "Manage incidents" 
2. Go to the incidents tab -> Schedule maintenance, set the parameters and click "Schedule now" 

Expected Results

User should be able to schedule the maintenance and access scheduled maintenances to see and edit them

Actual Results

When trying to create a new maintenance, initially a "Success" popup appears, followed by an authorization error - The user is then unable to access any of the created maintenances

Workaround

Giving users the "Incident manager" permission gets around this, but does not seem to be the intended way this should function.