Building a lock:sync command

[nterbogt]

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I would like this command from a CI environment point of view. If creating a multidev for a pull request, it makes sense that you can sync the lock from the source environment also, otherwise you have a security issue. i.e. `dev, test and live' are locked but any multidev built by build tools is public.

I considered extending multidev:create with --with-lock or similar but thought a general command to do this would be more useful.

[nterbogt]

lock:clone might be a command more consistent with the rest of terminus?