Document set-up of observability in code, for example to change the endpoint location

[tjquinno]

Environment Details

• Helidon Version: 4.x
• Helidon SE or Helidon MP SE
• JDK version:
• OS:
• Docker version (if applicable):

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Problem Description

With the introduction of observability into Helidon 4, the doc now does not show how to control the settings programmatically for metics, health, etc.

For example, there is no illustration of how to change the endpoint address.

From an internal Slack thread courtesy of @romain-grecourt

WebServer.builder()
        .port(8080)
        .addFeature(ObserveFeature.builder()
                            .addObserver(MetricsObserver.builder()
                                                 .endpoint("/metrics")
                                                 .build())
                            .build())
        .build()
        .start();