Find uWSGI command-line option to increase number of workers

[tschaffter]

Add this option to the configuration file or docker-compose.yml

To address nlpsandbox/support#1

[tschaffter]

Notes

• A magic rules mentioned by the uWSGI doc is number of processes = 2 * number of CPUs. Well they actually say that one should not trust this magic number and instead try and adapt.
• Another point to consider is that currently the controller annotates notes sequentially and do not perform concurrent request.
• The minimum number of process should be equal to the number of submissions that the controller can run concurrently (currently 4).
• This comment say that they run 12 processes on 2 CPU cores.
• As an initial rule, I propose number of processes = min(max number of concurrent jobs * 2, 6 * number of CPUs). Monitor the performance of the data node and then consider updating this rules if there is an issue.