[EuiRange] Value thumb tooltip should accept custom input

**Requestor**

Design: @jovana-andjelkovic
Engineer: @itamarbadass

**Problem Statement**

Currently the slider thumb shows its position in the slider (0-100) instead of the value the slider is showing. In AutoOps case, we're using slider component as time slider, and the tooltip is expected to show the timestamp value for its position.

**Proposed Solution**

**Use Case**

AutoOps time slider, in Shards view, is our current example. There's also time slider on dashboards that uses dual-range, however the tooltip is hidden there.

**Value / Impact**

**Urgency**

We have a workaround, so not a blocker. It is possibly something that others are facing and we're unaware of it.

**Do alternatives or workarounds exist?**

Yes, we're using a custom css which makes the value's `font-size: 0` while inserting the custom time based value in `valuePrepend` property.

**Related code or customizations**

**Additional context (Optional)**

**Designs or Specs (Optional)**