Distribute ActionCable load/work

[kiragrammel]

Normally, ActionCable uses several workers to process messages. This could lead to the problem that the messages are not received in the correct order. Therefore, the synchronized editor (of the pair programming feature) could get quickly out of sync.

To solve this problem, the worker pool size was limited to one worker with 70435a5: config.action_cable.worker_pool_size = 1 in config/application.rb.

However, this change also introduces a potential performance / stability limitation, because only one worker processes now all messages. Hence, all messages are just enqueued and wait until being processed. Therefore, it is necessary to think about another solution.