[Lens] Dedicated compare chart

[AlonaNadler]

Currently, in order to compare 2 fields, users often have them on the same chart from different sides of the axis (horizontally or vertically)

To achieve that today users often do bucket script to multiply a series with *-1 we should have a dedicated chart for it where users can add 2 different fields and see them based on a common axis

Example:
metricbeats read.bytes vs write.bytes

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

There's a similar request here: #54582

[wylieconlon]

Another similar request came in here, for a vertical comparison chart: #83738

[wylieconlon]

I think the input requirements for this type of chart are different than the input requirements for standard XY charts. Specifically, I think we need exactly two series. So the two options are:

a. No break down by, just the axis & two numeric metrics. This works if we support filters for each number
b. This option is not currently possible, but we could source the data by using a bucketed aggregation with exactly 2 buckets, followed by an another aggregation with any number of buckets and one metric.

[ghudgins]

can do this now with formula but need to resolve this elastic-charts issue with negative values elastic/elastic-charts#1280

...consider comparison example in formula in product doc

...could also suggest this visualization method if we improve suggestions as well

[markov00]

AS probably described by Graham, this can be achieved with formula