uniform UI for user to avoid interactive prompting

Extract from https://github.com/dandi/dandi-cli/issues/48#issuecomment-611785187 and inspired while reviewing #616 .
ATM for `--sync` operation we will seek user confirmation for destructive operation. But in many cases it would be expected and client might be used non-interactively. We should come up with some uniform way to interface it.

I would suggest `--yes` with choices applicable to the operation (e.g. `"delete"` for #616) and `nargs=*` or alike, so saying `--yes` would provide confirmation for all prompts (well, we could also make it explicit with `--yes all` or alike).

WDYT @satra @jwodder