[Lens] Formula: provide fitting function for missing/null values

[dej611]

Describe the feature:

A way to provide a fitting value for formulas would be useful to cover those cases where the ES gap_policy is used.

While in Visualize the Advanced JSON input provides a way to pass the { "gap_policy": "your-value" } json, there's currently no way to do that in formulas.

Imagine the following formula:

overall_average(average(field))

Now the overall_average function will skip all the empty buckets and compute the average only for those buckets who have a value.

The fitting value feature should resolve that by enabling the user to pass the type of fitting to use for the average computation.

[elasticmachine]

Pinging @elastic/kibana-vis-editors (Team:VisEditors)

[flash1293]

+1 https://discuss.elastic.co/t/lens-graph-formula-missing-fit-carry-ability-in-a-formula-summing-up-multiple-indexes-with-sparse-data/311192

[markov00]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner.