Add ability to display a value in legend & sort (defined by user) legend items by this value

[markov00]

Is your feature request related to a problem? Please describe.
The legend should show the last bucket value for each series in the list. This is currently used in TSVB to display the latest value and/or to display the current hovered value.
We should probably add this as a configurable feature, that can be disabled when not needed.

Describe the solution you'd like
On the right of each series title on the legend, we can add a space dedicated at displaying the latest bucket value and/or the hovered value of each series.

Describe alternatives you've considered
n/a

Additional context
n/a

Kibana Cross Issues
n/a
Checklist

• this request is checked against already exist requests
• every related Kibana issue is listed under Kibana Cross Issues list
• kibana cross issue tag is associated to the issue if any kibana cross issue is present

[markov00]

🎉 This issue has been resolved in version 3.9.0 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

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