Describe the feature:
Allow a user to configure a drilldown-style action from a legend series taking the selection into another part of Elastic (like a Dashboard)

Describe a specific use case for the feature:
Analytics Author
When I am authoring an XY visualization with a breakdown by (and legend)
I need to add a custom action to the legend
So I can take an entire "series" into a tailor-made Dashboard for analyzing that series

Solution Developer
When I am composing my solution and using Lens Embeddable
I need to add a custom action to the legend
So I can take an entire "series" into another part of the solution focused on analyzing that series

Side note: I'm writing this issue as a follow-up to a discussion had with @stephmilovic who was very excited that @stratoula had added the filter series options to legends