Sync Debug Metrics/Tools (#646)

* Get message requester queue size

* New metric MessageRequestQueueSize

* Add Prometheus exporter for MessageRequestQueueSize

* Fix msgRequester metrics measurement

* Update local_dashboard with msgRequestQueueSize panel

* Add DBStats method to msg layer tangle

* Measure DBStats in metrics plugin, report via Prometheus

*  Add "Messages in DB" chart to local grafana dashboard

* Fix DBStats method

* Refactor DBStats metrics collection, update default params

* print DBStats() func ints

* Compare iterative and incremental DBStat data collection

* Add messageCount and solidMessageCOunt to /info webapi endpoint

* Cleanup metrics and prometheus plugin

* Update /info webapi data collection

* Fix too many relases in message tange

* Small fixes

* FIx avgSolidificationTime metrics

* Fix avgSolidificationTime calc

*  "Add Average Solidificaiton Time" Chart to Grafana Dashboard

* Restore metrics plugin parameters

*  Add synced status to node dashboard

* Make scheduledRequestsMutex a RWMutex

* Add client lib tool for past cone exist verification

* Update local_dahboard for docker-network

*  Introduce tools endpoint for webapi

 - disabled by deafult
 - contains utility api-s, e.g., "tools/pastcone" that given
   a message ID, checks if all messages in the past cone are
   present in DB down to genesis
 - Add PastConeExist() client api method

* Get rid of debug prints

* Small fixes

* 

 Update grafana dashboards

* Update client/tools.go

Co-authored-by: Jonas Theis <mail@jonastheis.de>

* PR review updates

* Remove unused variable in metrics/message

Co-authored-by: Luca Moser <moser.luca@gmail.com>
Co-authored-by: Jonas Theis <mail@jonastheis.de>