gradle aggregate coverage report

[rmuir]

Description

Currently, when running the build (e.g. gradlew coverage) you get a per-module report.

Ideally we'd produce an aggregate report (similar to what black magic jenkins is doing: https://ci-builds.apache.org/job/Lucene/job/Lucene-Coverage-main/lastSuccessfulBuild/jacoco/

It would be great to also print the summary to the console (same as #11837).

This would be nice, a single artifact of the code coverage for a build. For example, It could eventually be archived as a github action to help us better inspect PRs.

[zhaih]

@rmuir I can work on it if you don't want to do it right now?

[rmuir]

@zhaih please take it!