Problem Description: Adding Execution Environment fails for users without permission in UI. Permission error isn't displayed and nothing happens.

Reproduce:
1. create a test user without permissions
2. go to `/ui/containers`
3. click on `Add execution environment`
4. fill out the form  (e.g. Name: `eetest`,  Upstream name: `upstreamtest`, Registry: `docker`) 
5. Click the `Save` button

Proposed Solution: Hide the `Add execution environment` button when the user doesn't have permission (`Create new containers`). That way users can't visit the `Add execution environment` modal.