Add configuration to disable queue healthcheck

[sbrossie]

We currently export a health check for our KB internal queues based on some HoltWinters metrics we compute.

We have had reports of companies complaining about false positives, where their deployment is reported as unhealthy while the situation is expected (e.g monthly bill run where entries spike up).

We would like to add a way to disable the check - and simply return true - based on some configuration.

[sbrossie]

See this issue killbill/killbill#1904

[reshmabidikar]

Addressed in #155. Closing this issue.