SOLR-16782: Export tool should export in JSON that matches Solr Import Format

[epugh]

https://issues.apache.org/jira/browse/SOLR-16782

Description

Export tool only supports Javabin and JSONL, not JSON... We would like to have that to be able to import docs directly!

Solution

Add JSON format... Make it the default format as JSONL is somewhat special purpose...

Tests

extended existing tests.

Checklist

Please review the following and check all that apply:

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

[epugh]

Okay, I think this is ready for review.. With slicked up examples in ref guide. I tested the round tripping...

[janhoy]

Did not review, but makes sense.
However, for huuuge exports, jsonl makes sense since it is much easier to parse/stream line by line and won’t kill your editor. Probably solr’s json loader handles normal json in efficient way. But would be just as interesting to add support for jsonl to /update

[epugh]

@janhoy I spiked out JSONL for solr streaming expressions... SO you can split the big doc and have multiple loaders all running ;-) For similar reasons... I had an interesting conversation with Christopher Ball about this at Haystack ;-)