metrics: New circuit related metrics relay side

This is tied to sponsor 112 with tpo/network-health/team#299 (closed).

We need to implement these:

• Number of circuit collapsing as in DESTROY coming from the opposite direction.
• Circuit being closed due to protocol violation.
• Anything around drop cells. A rate, what type, etc...

Basically, keep counters of those events and expose them on the MetricsPort.