SOLR-15788 Remove configset/sample_techproducts_config from being used in unit tests

[epugh]

https://issues.apache.org/jira/browse/SOLR-15788

Description

Break link between our example configset and the run of the mill unit testing.

Solution

introduce a solr/solrj/src/test-files/solrj/solr/testproducts configset based on the old techproducts configset, and then start removing files that aren't used by the solrj tests.

Maybe it should be called collection2 instead?

Tests

Running the unit 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