[Transform] add support for boxplot aggregation

Description

Contributor guide

Tech stack

java

Domain

backenddata

Issue type

feature

DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.

3

Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.

1-2 days

Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.

stale

ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.

mostly clear

Prerequisites

Understanding of Elasticsearch aggregationsFamiliarity with transform featureJava development environment setup

Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.

20

Research direction

Investigate the existing transform aggregation implementations in the Elasticsearch codebase, likely in the 'transform' module. Review how other aggregation types (e.g., percentiles) are supported and follow the pattern to add boxplot aggregation. Check the comments on the issue for any additional requirements or design decisions. Look at the test files for existing aggregation support to understand expected test coverage.