shell exec possibility

As a user/operator I would like to exec a shell command, like for instance `ls -lR /etc/cloudstack/extensions/` from the cmk prompt, to get some info to use in a command in cmk.

Start by locating the cmk prompt command-dispatch entry point and any existing command execution tests. Determine the expected handling and completion criteria for running a shell command from the prompt, including how its output is exposed to subsequent cmk commands.

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