Let me specify an external command to be run for each chat response

[MikeRich88]

After it's finished generating each chat response, let me specify an external command to be executed.

The text can be represented with some placeholder such as "{}", and if there is no placeholder specified, then the response should be passed into STDIN. (Which can be ignored if you don't actually need to use the response in the command).

This would be extremely useful for example, on macOS you could pass the response to the "say" command, and now the responses are spoken.

I could not find any feature at least in my version: 5490 (fef693d) which is the absolute latest version as of right now. (looked for command, execute, program, external, etc. in the llama-cli help output).

Maybe one of the other llama-* commands does this, but I'm new at this and there's so many of them, so I think a simple option on llama-cli would still be useful and more easily discoverable.