Clearer X-Axis description of histogram and flamegraph panel

[simonswine]

I think we should make it clearer what the X-axis represents in the histogram and the flame graph represent:

While the histogram's x-axis is time, the flamegraph's x-axis unit is the is the percentage of the resource used.

I wonder if we need to do something before the obscon mile stone, wdyt?

For reference on the top the histogram and at the bottom the flamegraph as of right now:

[joey-grafana]

Closing this as completed. Summary: we added the unit values to each block in this pr, and explored adding a scale above the flame graph in this pr, but ultimately didn't go with the scale as it seemed like adding the unit values to each block was enough.