can't setup `cloudevents.serializer.event_format` in quarkus

Hello everyone, I want to express my appreciation for the fantastic work you're doing!

I've noticed that Quarkus reactive Kafka replaces all underscores (_) with periods (`.``). Here's a code snippet from quarkus code to illustrate this:

private static void extractConfigKey(Config config, JsonObject json, String originalKey, String prefixToStrip) {
    // Transform keys that may come from environment variables.
    // As Kafka properties use ".", transform "_" into "."
    String key = originalKey;
    if (key.contains("_") || allCaps(key)) {
        key = originalKey.toLowerCase().replace("_", ".");
    }
    // ...
}

This transformation is causing an issue for me when trying to pass event_format in the application.properties file:

/**
 * The configuration key for the {@link EventFormat} to use when serializing the event in structured mode.
 */
public final static String EVENT_FORMAT_CONFIG = "cloudevents.serializer.event_format";

Is there a way to also support event.format, or do you have any suggestions for a workaround? Your insights would be greatly appreciated!

Start with the extractConfigKey method and the EVENT_FORMAT_CONFIG constant shown in the issue, then trace how reactive Kafka maps configuration keys. Determine whether event_format can be configured without being transformed incorrectly, or whether a documented workaround is needed; done means the setting works reliably in application.properties.