We need a controller method that can call MetadataWranglerOPDSLookup.run_self_tests(). We also need admin code to show a "Metadata" tab on the troubleshooting page, call that controller method, and render the results.

Keep in mind that these SelfTestResults may have a relevant associated "collection". Previously SelfTestResults either had no collection, or the collection was implicit (because the collection itself was the thing being tested).