Overhaul `nix flake update` and `nix flake lock` UX (cherry picked from commit 12a0ae73dbb37becefa5a442eb4532ff0de9ce65) Change-Id: Iff3b4f4235ebb1948ec612036b39ab29e4ca22b2
Iff3b4f4235ebb1948ec612036b39ab29e4ca22b2