SOLR-15570: Include declared but unused fields from the schema in table metadata

[thelabdude]

https://issues.apache.org/jira/browse/SOLR-15570

Description

Combine fields from the luke endpoint + schema to include declared but unused fields from the schema in table metadata

Tests

simple unit test added

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