Add save_as functionality to duplicate entities

[aminalaee]

Discussed in #370

^{Originally posted by CrispyCrafter November 7, 2022}
We've been using SQLAdmin internally to manage a large fleet of IoT devices.
One pain point at the moment is the inability to duplicate fields.

Typically a batch of devices would be provisioned in the same way, with minor differences to device IDs

How would one go about including a duplicate button, inline with view and edit?

[aminalaee]

After #373 it's easier to implement the save_as functionality.