IssueTracker

While we can define document factories for classes we can't easily add annotations to (i.e. protos), there doesn't seem to be a way to actually register custom factories with the system. The closest I got was:

```
object DocumentFactory : DocumentClassFactory<ExternalSearch> {
        init {
            val instance = DocumentClassFactoryRegistry.getInstance()
            var factories by DocumentClassFactoryRegistry::class.java.privateField()
                .asProperty<DocumentClassFactoryRegistry, MutableMap<Class<*>, DocumentClassFactory<*>>>(
                    instance
                )
            factories.put(ExternalSearch::class.java, this)
        }
    }
```

Maybe I could make expose an  AppSearchDocumentClassMap implementation from somwhere, but that seems like a lot of work.