Improve compute.log readability

[lubennikovaav]

Now we merge compute_ctl and postrgesql logs into one stream.

in both prod and pytest environments

It is sometimes convenient to have them in chronological order - if they were separate logs you'd need to open both logs and compare the timestamps.

But this complicates debugging postgresql issues.
Also this blocks issues about showing postgresql logs to user such as #4075

Let's discuss possible improvements

• split log streams
• write postgresql log to both logfile and stderr (merged stream)
• improve log message style (format, prefixes etc)

cc: @MMeent, @hlinnaka

[Omrigan]

See also neondatabase/autoscaling#578