[Lens] Line and area stepped curve option

[wylieconlon]

The main remaining type to support is Stepped.

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There are some basic curve options that users should be able to select for each line in Lens. This option should be presented for each line series, so that you could mix curve types if you choose to.

However, the number of options available in Elastic charts is higher than what we should support.

In the Visualize line chart, we support three options only:

• Linear
• Smooth
• Stepped (equivalent to Step after)

Of the curve options that are available with a demo here, we should support these:

Curve type	Special logic
Linear	Default
Curve natural
Curve catmull rom
Curve step after	Should hide the point
Curve step before	Should hide the point

This leaves the following curve types unsupported:

• Monotone X
• Monotone Y
• Basis
• Step
• Cardinal

cc @markov00

[elasticmachine]

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

[markov00]

Elastic-charts has already all these curve types for LineSeries and AreaSeries see https://elastic.github.io/elastic-charts/?path=/story/line-chart--curved-with-axis-and-legend

[wylieconlon]

The main remaining type to support is Stepped.

[ghudgins]

stepped would be an additional option and require us to change the curve from an on/off to a dropdown - https://github.com/elastic/elastic-charts/blob/master/storybook/stories/area/20_stepped_area.tsx#L435

[markov00]

closing in favour of #154410