`repro`: rename `--dry` to `--no-exec`

[jorgeorpinel]

I think --dry is reserved for commands that are read-only and make no actual changes to the repo state
- @dberenbaum

repro is not a read-only command in that sense. So should its --dry option be renamed --no-exec then? Consistent with run and import(-url)

Originally posted by @jorgeorpinel in treeverse/dvc.org#3345 (comment)

[pmrowla]

repro --dry is read-only though?

run --no-exec and import --no-exec are not read-only because they still make changes to the repo state (even with --no-exec the commands still write changes to dvc.yaml and .dvc files)

[pmrowla]

I think @dberenbaum's original point was that we use --dry when it makes the given command read-only (not when the original command itself is always read-only)

[jorgeorpinel]

Ah. I think you're right. repro --dry is read-only indeed. For consistency I'd still recommend --no-exec but thinking about it, --dry is quite different since it prints a summary of what would happen, unlike run/import --no-exec. OK you win again @pmrowla -_-