ability to set privoxy debug logging

[andy-nai]

Currently it's set to 1 which logs all requests and sends to docker stderr and 4096 which shows a start-up banner.
I think we should have these by default: 1024, 4096 and 8192 and provide an option to enable 1.

docs here: https://www.privoxy.org/user-manual/config.html
(section 7.3.1)

[andy-nai]

and perhaps not log 1 to stdout, maybe to a file instead.