Add general logging to appcli

[david-homley]

It would be nice to have appcli log its usage executions and resulting output, as currently the only way to track past executions and output of an appcli application is by manually recorded the logs from stdout.

This would be useful to capture information about an appcli task or process that fails before the underlying application can log.

[al-jeyapal]

I think always capturing stdout to file would probably be good. I.e. each time it's invoked. Ideally it would handle its own log rotation etc as well.

[thomas-anderson-bsl]

We'll need to consider the design to avoid leaking potentially sensitive data (passwords etc).