Add a 'Read Path' dashboard

[arodrime]

As part of our idea for MCAC dashboards design, we need 2 kind of dashboards, for 2 distinct usages:

• Overview Dashboard(s) - To detect anomalies. That's the dashboard where alerting can/should be set up. Some overview dashboards could be more oriented towards total numbers to ease technical talks preparation or marketing.
• 'Themed' Dashboards - To troubleshoot or optimize a specific aspect, internal, ... Dashboard are in this case grouped by 'theme' like Read path, Write path, client connections, entropy...

In that idea, this ticket's goal is to create a themed dashboard, for metrics impacting the read path.