Sciond should export prometheus metrics. This is especially useful when it's running on an infrastructure node.

Potential metrics:

• client requests by type (path, iainfo, revnotify, etc)
• path requests by ISD (and possibly by IA)
• total request latency (from request to response)
• sent requests by type (pathreq, certreq)
• PS/CS response latency
• timeouts/errors