Documentation out of date regarding log retention management

[shinmyung0]

The documentation around DB properties here states:

...In addition, all build logs are stored in the database. This is the primary source of disk usage. To mitigate this, users can configure build_logs_to_retain on a job, but currently there is no operator control for this setting. As a result, disk usage on the database can grow arbitrarily large.

But there are configuration settings for controlling logs retention:

--default-build-logs-to-retain=                                                    
--max-build-logs-to-retain=                                                                
--default-days-to-retain-build-logs=                  
--max-days-to-retain-build-logs=