Use propolis client directly for serial console

[rcgoodfellow]

The following code is copy pasta from the propolis client implementation with a small modification to use ^q for escaping the serial session (and thereby allowing ^c through to the VM)

https://github.com/oxidecomputer/falcon/blob/main/lib/src/cli.rs#L406-L543

Now that the propolis client CLI machinery is getting a configurable escape sequence, we can just use that implementation directly and configure the tunable escape sequence to be ^q to maintain the current falcon behavior.