Implement Kahan Summation algorithm

[zkscpqm]

Currently the Sum aggregation was simply done with += which can lead to inaccuracies when working with high-precision values.
The Kahan Summation algorithm checks for such inaccuracies by performing the sum and keeping track of lost precision points.

Edit 1: Updated to account for new values being larger than running sum

[elasticmachine]

Pinging @elastic/es-analytics-geo (Team:Analytics)

[nik9000]

For what it's worth the sum does use Kahan on the data nodes. This is for rollup. @csoulios might be the best to have a look.

[csoulios]

@zkscpqm thank you for contributing this improvement.

There is already an implementation of KahanSummation implemented in CompensatedSum

Please have a look

elasticsearch/server/src/main/java/org/elasticsearch/search/aggregations/metrics/SumAggregator.java

Line 64 in 9129dcd

final CompensatedSum kahanSummation = new CompensatedSum(0, 0);

Do you think you could modify your code so that it uses CompensatedSum?

[pugnascotia]

@zkscpqm are you still interested in working on this PR?

[csoulios]

This PR has been idle for long.

Also, this feature has been implemented for the TSDB downsampling project (#87554)

Closing it.