Update commandlog parameters conf text to mention special value settings

[enjoy-binbin]

Earlier we described the slowlog-log-slower-than configuration option like this, we explicitly mentioned the special meaning of negative numbers (actually -1) and 0.

The following time is expressed in microseconds, so 1000000 is equivalent
to one second. Note that a negative number disables the slow log, while
a value of zero forces the logging of every command.
slowlog-log-slower-than 10000

And after #1294 we lost this text, we need to mention these values, we can mention the special number for all command log's configs, also it seems we should also mention slowlog-max-len.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 71.25%. Comparing base (af25a52) to head (3255881). Report is 68 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2074      +/-   ##
============================================
+ Coverage     71.02%   71.25%   +0.22%     
============================================
  Files           122      122              
  Lines         66171    66030     -141     
============================================
+ Hits          46999    47049      +50     
+ Misses        19172    18981     -191     

see 20 files with indirect coverage changes

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[enjoy-binbin]

@zuiderkwast This is quite small, do you want to review it?