Recolor IPv8 Health line when core is dying

[qstokkink]

These following two images show what happens to the IPv8/debug/health tab when the IPv8 health monitor scales between its min_update_rate and its max_update_rate.

Fine	Starting to die

When everything is fine this graph shows a happy green line. However, when the core is starting to die and suffer, there is also a happy green line. My proposition would be to dynamically adjust the color of the line between green and red, corresponding to the update rate being closer to min_update_rate or max_update_rate respectively. Something like this:

Fine	Starting to die

[qstokkink]

After reflecting on this, perhaps green is easier on the eyes, considering the black background.