Add fields option to rules to allow for runtime fields and others

[Goggin]

Description

Checklist

• I have reviewed the contributing guidelines.
• I have included unit tests for my changes or additions.
• I have successfully run make test-docker with my changes.
• I have manually tested all relevant modes of the change in this PR.
• I have updated the documentation.
• I have updated the changelog.

Questions or Comments

[jertel]

Thanks for the submission. I noticed you checked the box that you added unit tests, but I don't see any. Did you miss a commit?

[Goggin]

Sorry, you didn't miss anything. I did not include unit tests for this change. Would you like me to write some?

[jertel]

Yes, please. See base_test.py and loaders_test.py which already have unit tests that should be covering those existing functions. I think get_hits() may be called indirectly via run_query() in the unit tests. load_options() should be called directly in the existing unit tests.

[Goggin]

I have added tests, please let me know if there are any additional tests you think need to be added.