Make discriminator values easy to copy, e.g. by automatically adding a single-value enum to discriminators

[cmeeren]

When selecting discriminator values in the dropdown, there is no easy way to copy the value.

It would be nice if it was possible to easily copy the value.

Since the discriminator is in effect an enum, ReDoc could render an enum value equal to the currently selected option. For reference, this is the kind of enum rendering I am talking about:

Other solutions may also exist.