Admin: Add the functionality to duplicate maps

[jacobwod]

A common use case for administrators is to create new map configurations. Often, it is desired that the new map is similar to other maps in a certain setup, eliminating the need to manually set things like used projections, extent, common tools, etc.

The backend has had the ability to duplicate maps for a long time (it's always been part of the NodeJS backend). Until now, admins had to use the endpoint manually, by calling PUT /api/v2/mapconfig/duplicate/oldMap/newMap.

Now it's time to add this functionality to the UI as well.

This functionality is also mentioned in #650.

[sweco-semara]

@jacobwod SGI asked about this recently and before I had a chance to look deeper into this issue there was an implemented solution and already accepted PR. Great! Thanks. 🙂