Modify fix command to replace vars with replacements

[monopole]

We should at lease see how difficult this would be.

so running

kustomize fix

would, say:

• copying the kustomization and everything it referred to to a tmp dir
• running the build and saving the output to the tmp dir
• then (vars specific):
  • scanning all resources for embedded $VAR placeholders,
  • computing the target address for a replacement entry (where the $VAR was found),
  • replacing $VAR with some non-dollar, placeholder value that's legal (could be applied to the cluster)
    but perhaps unusual (e.g. the literal string 'placeholder', or the number 99999)
  • writing the modified resource files and kustomization files back to the tmp dir
• running build again to compare the new result to the old result
• if no change, copy everything back over the top of the real resources
• else report error and don't copy
• delete the tmp dir

kustomize fix does not do the copy and compare now, but it should have done so from the start, so part of this work fixes something that should already be there (and that could be peeled off into a different issue done b4fore this one)

[natasha41575]

Will work on it

[natasha41575]

Currently working on this and commenting to reflect discussion:

Rather than copying the directory, we will have this behind a flag (e.g. kustomize edit fix --vars), and it should output a diff between the previous and new output of kustomize build. In a git repository the changes will be easy to undo if the output is different.

[natasha41575]

closed by #3926