Support for Subscriber metricset ActiveMQ

[Linu-Elias]

Support for primarily PendingQueueSize in ActiveMQ package

• PendingQueueSize is actually not a metric for a Topic or Queue but this metric is of a Subscriber
• One topic can have multiple subscribers, and each subscriber has their own set of metrics.

Solution

We should add a new metricset "Subscriber" with couple of all subscriber metrics, Eg: DestinamtionName, subscriberName, PendingQueSize etc... So that the user can do an aggregation of the PendingQueuSize/topic.

[botelastic]

This issue doesn't have a Team:<team> label.