4.x: Use LevelChangePropagator in logback examples

[romain-grecourt]

Environment Details

• Helidon Version: 4.0.0-RC1

---

Problem Description

When using jul-to-slf4j bridge with logback, the performance cost can be mitigated by using LevelChangePropagator.

<configuration debug="true">
  <contextListener class="ch.qos.logback.classic.jul.LevelChangePropagator">
    <resetJUL>true</resetJUL>
  </contextListener>
   <!-- rest of the configuration file .... -->
</configuration>

---

• We should update examples/logging/slf4j to use it so that we demonstrate a best practice.
• We should update the logback.xml snippet in the blog article
• We should be setup the bridge using logging.properties instead of code as that is a "drop-in" and can be used regardless of the Helidon flavor:

logging.properties:

handlers=org.slf4j.bridge.SLF4JBridgeHandler