`kgtk lift` merge multiple columns

[CraigMiloRogers]

kgtk lift merge should be able to lift multiple columns so long as only a single label value is involved.

This requires a generalization in which we specify the column sourced from the label edge per lift transform. This needs another option with nargs='*'.

Another enhancement would be to specify multiple columns to match between the input edge and the label edge, or perhaps a language match.

This is a low priority issue.