[jkarneges]

This adds optional prometheus metrics serving, along with an initial component-specific metric (total requests).

# HELP api_log_messages_total Total number of log events emitted by level
# TYPE api_log_messages_total counter
api_log_messages_total{level="debug"} 0
api_log_messages_total{level="error"} 0
api_log_messages_total{level="info"} 2
api_log_messages_total{level="trace"} 0
api_log_messages_total{level="warn"} 0
# HELP api_requests_total Total number of requests processed by api
# TYPE api_requests_total counter
api_requests_total 5