Add prometheus metrics

[masih]

Add metrics for:

• Number of providers
• Reframe response latency tagged by response code
• Find response latency tagged by response code
• Backend response latency tagged by backend name

Once metrics are implemented in go, manifests need to be updated to add prometheus pod monitor, and the deployment needs to be updated to export the debug and metrics server if it is separated from HTTP server.

[willscott]

the remaining metric we need to close this out is Backend response latency tagged by backend name