Allow duplicating MQTT devices in Gladys + make feature properties editable

[Terdious]

Following up on @bong101’s request:

@bong101

Feature description
In Gladys, it would be nice to be able to duplicate scenes, MQTT devices, etc. so I can edit the new ones. I use fictitious MQTT devices that serve as entry points for scenes and it’s a real pain for me every time to edit the properties (of scenes or of MQTT devices).
Strangely enough, in the MQTT integration, some fields can no longer be modified once created.