[Maps] Dynamic style by document age

[nickpeihl]

Describe the feature:
Allow dynamic styling based on time fields relative to the selected date range for the visualization.

Describe a specific use case for the feature:

Imagine looking at live flight data positions over a period of time (say 1 hour). You could have several documents on the map showing the recorded positions. It would be nice to have a way to style these (color and/or symbol size) by the age of the @timestamp relative to the selected time range. So an older position (upper left, in the screenshot) might be a lighter shade of red than a newer position (lower right).

[elasticmachine]

Pinging @elastic/kibana-gis

[alexfrancoeur]

Copying a comment over from my duplicate issue that I just closed:

Further more, it would be great if the future geo_line aggregation (elastic/elasticsearch#41612) could be dynamically styled in this fashion as well. One end of the line being light or transparent and the most recent part being darker.

[alexfrancoeur]

🍾🍾🍾