Duplicate Switcher creation causes incosistency

[petruki]

Describe the bug
It is possible to create Switchers using the same name within different Groups.
This may cause inconsistency when calling as the API will always process the first one.

To Reproduce from Switcher Management
Steps to reproduce the behavior:

1. Create a Switcher in one group
2. Create another Switcher with the same key as the previous step in a different group

Expected behavior
The API should return an error not allowing creating Switchers with the same key under the same Domain