Lotus metrics

[turuslan]

Add more metrics like lotus/metrics/metrics.go which can be collected by our node.

Our node already has prometheus metrics for counter and gauge. Maybe we need to implement buckets for histogram and summary. Integrating external library may be an option too.

UPD. Didn't find summary metrics usage in lotus yet.

UPD. Switching to prometheus-cpp.

not implemented:

• info{commit version}
  • Add version and commit hash #532.
• peer/count
  • does cpp-libp2p provide disconnect event?
• *block/failure, *block/success
  • *blocks are not validated, currently measuring tipset vm.
  • Validate blocks #539.
• block/validation_ms
  • blocks are not explicitly validated (tipset vm time is other metric vm/applyblocks_total_ms).
  • Validate blocks #539.
• message/failure, message/success, message/validation_ms
  • messages are not explicitly validated.
• mpool/getnonce_ms, mpool/getbalance_ms, mpool/addts_ms, mpool/add_ms
  • no corresponding functions or they are trivial.
• mpool/push_ms
  • api/request_duration_ms {endpoint=MpoolPushMessage} is used instead.
• block/delay
  • is it for SyncSubmitBlock and/or pubsub?
  • does it have timeout?
• pubsub/published, pubsub/delivered, pubsub/rejected, pubsub/duplicate, pubsub/recv_rpc, pubsub/send_rpc, pubsub/drop_rpc
  • does cpp-libp2p provide these metrics?