Allow execution of shell commands [Edit: without the need for a `!` prefix]

In my use of the aws-cli/SAWS I find I'm frequently interacting with basic shell commands. aws-shell does not allow me to do this, which seems to force me to pop in/out of aws-shell.

This is supported on SAWS:


See: https://github.com/donnemartin/saws/issues/8

Start with the SAWS issue reference and screenshot to confirm the intended shell-command behavior. Locate aws-shell’s command handling, then verify that ordinary shell commands execute without leaving the shell; add relevant coverage if the project provides it.

Written by the indexing model from the issue text.