[MARTIFACT-6] create buildinfo file in root artifact instead of last module

**[Hervé Boutemy](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=hboutemy)** opened **[MARTIFACT-6](https://issues.apache.org/jira/browse/MARTIFACT-6?redirect=false)** and commented

when used with multi-modules build, current implementation creates the buildinfo file in the last module (that will be deployed to repository, more precisely)
This is because buildinfo records fingerprints/hashes of the result of the build, then artifacts to be fingerprinted are available only at the end of the build

It works, but it adds a level of complexity to find the buildinfo file

It would be a lot easier to use if buildinfo could be generated (and eventually deployed) in root directory

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**Affects:** 3.0.0

**Issue Links:**
- [MARTIFACT-8](https://issues.apache.org/jira/browse/MARTIFACT-8) multi-module: copy aggregate buildinfo to root target

**Remote Links:**
- [discussion on plugin improvements
](https://github.com/jvm-repo-rebuild/reproducible-central/issues/20)

Start by tracing how the buildinfo file is generated during a multi-module build and why the final module receives it. Review the related MARTIFACT-8 issue about copying an aggregate buildinfo to the root target. Done means the aggregate buildinfo is available in the root directory, with deployment behavior addressed as specified.

Written by the indexing model from the issue text.