exp run: rename --temp?

[jorgeorpinel]

Extracted from #5814 cc @dmpetrov
"The --temp option name is a bit confusing. I'd prefer something like --background."

We actually discussed the term "background" recently (for docs) and decided that it's misleading: exp run --background may sound like $ exp run & (on Linux). In reality there's no background process, but rather the experiment runs "outside the workspace" — the phrase we use in docs. That said, "temporary" is also not the best concept.

Ideas: --outside ,--foreign, or --adj(acent).

Or if we're sticking with the current implementation-detail-based name, maybe --tmp (no e, as in .dvc/tmp)

[jorgeorpinel]

Users may understand that --queue runs in "tmp dirs" though so that's an argument for keeping --tmp. E.g. #5800

[jorgeorpinel]

Unless --tmp runs are made the default again, rel. #5750 (comment), in which case the option would no longer exist this issue can be closed.