cmd/cue: add "hoist" command

[cueckoo]

Originally opened by @mpvl in https://github.com/cuelang/cue/issues/7

Implement cue hoist to extract templates from concrete data definitions. One could see this as cue trim in the opposite direction.

This can be implemented using the known anti-unification algorithm. It probably makes sense, though, to disregard disjunctions or to limit the number of elements.

[myitcv]

Linking to https://github.com/cue-lang/cue/discussions/2231 because apparently GitHub does not create the linkage between issues and discussions.