Provide parameters to customise log output

[michaelsauter]

There should be a way to customise the log output somewhat. In particular, the following flags to tkn pr logs look interesting:

--prefix         prefix each log line with the log source (task name and step name) (default true)
--task strings   show logs for mentioned Tasks only
--timestamps     show logs with timestamp

Either we should allow to pass any number of params to the command, or we should provide specific params for some or all of those params.