Title: Dynamic Modules: Support Metrics with Tags

Description:
Currently, dynamic modules support metrics without labels. However, many real-world use cases may want to emit metrics with labels, some of which whose values may not be known in advance. A consequence of this is that the full metric name including the tags may need to be created during HTTP processing rather than HTTP filter factory construction.

This issue tracks the work to support these metrics.

Relevant Links:

• The Istio stats filter as an example of how stats are used in custom filters