Add Minimum Queue Size Threshold to Metrics API

[MHillyer]

As a MailOps administrator I use the metrics API to monitor my servers looking to see if any queues are getting too large so I can investigate further.

My monitoring tool of choice is overwhelmed by the sheer number of metrics returned because I get data on each and every queue that is active, when I only care about larger queues.

If I can pass an argument to say what the smallest queue size is that I care about, I can significantly narrow down how much data the API returns, without losing any relevant information for my monitoring purposes.

For example, I could pass that min size is 1000 and any queues smaller than 1000 messages would not be returned by the metrics API.