Allow custom values for EuiRange

[cchaos]

Right now, the range component only supports the typical step increments supported by the html input type="range" component. However, there are use cases where the steps may be exponential though visually they'd be best displayed equidistant.

Cloud example:

[thompsongl]

I'm curious about the rationale for using EuiRange in the example above instead of a radio group.
Especially when comparing to the radio group directly below, the intention and interaction are almost identical.

[cchaos]

@gjones ^^

[gjones]

@thompsongl You're correct, they are similar from an under-the-hood, technical standpoint. Although I may take some convincing that using radios is the most effective way to present 7-10 linear options.

I think what matters here is user perception, scaling your cluster is a huge benefit of Elastic Cloud and we felt the best way to communicate the ease of increasing and decreasing your RAM is allowing the user to play around with a slider and watch your deployment architecture update in real time.

Additionally there was a marketing push behind the project, which was itself externally called "Sliders", that painted us in a bit of a corner too 😃.

I hope that makes sense and gives a bit of background, but I am always open to feedback.

[thompsongl]

Right on. I can see especially in terms of space constraints how this could be a win.
My read is that there would be no scenario in which the slider is not locked to the steps, correct? Regardless of the context, it doesn't seem to make sense for this type of slider to allow for selecting values between the intervals.

[cchaos]

This was added via #1485