[Lens] Dimension editors

[flash1293]

Provide dimension editors for value, terms date_histogram, filter ratio and common metric aggregations (min, max, sum, avg).

Filter ratio isn't supported in the current editor but would be a nice addition. It takes two queries and outputs the ratio of its counts (optionally ratio of some metric sub aggregation)

[elasticmachine]

Pinging @elastic/kibana-app

[wylieconlon]

@flash1293 After some discussion this morning we're thinking that these dimension editors should also provide users with a "Custom Label" option that defaults to the operation label. This is a feature that should exist on all columns, so it makes sense to put it in the dimension editor.

[flash1293]

SGTM @wylieconlon I will add this to my current work about dimension editor flow.