SOLR-15152: Export Tool should export nested docs cleanly in .json, .jsonl, and javabin

[epugh]

Description

Export tool says it uses json, but it's actually a json lines format. It ignores anonymous and nested docs.

Solution

• Tweaked the writer to properly handle anonymous and regular nested docs when exporting data.
• Renamed the existing json format to jsonl, and introduced a proper json format.
• Introduce explicit DocSinks per format, json, jsonl, and javabin.
• Create new configsets for testing under nested/anonymous and nested/regular for testing.
• added nested products example that was used in the Ref guide to the example/exampledocs/office_products.json.
• Changed sample_techproducts_configs to used explicit nested docs, not anonymous nested docs, and then fixed various tests that assumed anonymous children. This was tough!
• Updates to the Ref Guide.

Now, with the json format you can export and then reimport the Solr docs, including with child docs!

Tests

I've added a new TestExportToolWithNestedDocs, and extended the existing TestExportTool tests. The setup for the tests was quite different, so I didn't make them all one file. I've updated the existing tests that

Checklist

Please review the following and check all that apply:

• [X ] I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• [ X] I have created a Jira issue and added the issue ID to my pull request title.
• [ X] I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• [ X] I have developed this patch against the main branch.
• [ X] I have run ./gradlew check.
• [ X] I have added tests for my changes.
• [ X] I have added documentation for the Reference Guide

[epugh]

There is a lot of good commentary on https://github.com/apache/lucene-solr/pull/2356 that should be reviewed!

[epugh]

I'm working up the energy to tackle this again!

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