Use `--` to exec a command

[ipmb]

I'd like to use assume <profile> --exec ..., but it can be hassle trying to escape more complex commands that use quotes.

The double dash is a standard for splitting arguments in these scenarios and is used by tools like chamber and aws-vault which need to inject environment variables into the following command.

Would you consider something like:

assume myprofile -- command --with --flags=1

or

assume myprofile --exec -- command --with --flags=1