Query Analytics Dashboard: Mouse-over crosshair shows value on sparklines

The problem:

When you looking into QAN sparkling it's hart to correlate with different spikes in different dashboards/sparklines 

Proposed solution: use a similar solution to what we use in grafana  - shared crosshair for sparklines in QAN 

Where:

• Overview 
• Details section

Questions:

• should we change the color to red to reflect other crosshairs on grafana?

DOC: 

• Update QAN doc with new feature

Example: (maybe  white color ?)