DOCS: 4.x Health Checks SE and MP

[ljamen]

Problem Description

We need to update docs for 4.x

• update health.adoc for MP
• update health.adoc for SE
• update health.adoc guide for MP
• update health.adoc guide for SE

Guidelines

• Make sure any fixes from SE 3.x are forward ported to 4.x DOCS: SE Diffs 3.x to Main *.adoc  #7515
• Make sure any fixes from MP 3.x are forward ported to 4.x
• Initial focus is on correctness
• Record migration impact in this issue

Migration Impact

Summarize incompatibilities between Helidon 3 and Helidon 4.

• MP: To set the path for the health endpoint, use the health.endpoint config key instead of health.web-context.
• SE: To set the path for the health endpoint:
  • Use the features.observe.observers.health.endpoint key instead of health.web-context.
  • Use the endpoint method on the HealthObserver.Builder type instead of the webContext method on the HealthSupport.Builder type.
• SE and MP: To set up a non-default socket for health (and all observability endpoints) use the server.features.observe.socket config key:

  server:
    sockets:
      - name: "admin"
      - port: 8081
    features:
      observe:
        socket: "admin"
  

• SE: The HealthSupport type is replaced by the combination of ObserveFeature and HealthObserver. See the doc for details.
• SE: The default health endpoint is now at /observe/health instead of /health as in 3.x.
• SE: SE applications now use the io.helidon.health.HealthCheck and ...HealthCheckResponse types instead of the counterpart types from MicroProfile Health.
• SE: Adding the helidon-health and helidon-health-checks dependencies to a project automatically adds the built-in health checks and the health endpoint to the application; application code no longer needs to explicitly add health to the application unless it also disables WebServer.Builder.featuresDiscoverServices.

Summarize actions customers must take to migrate code
OK to reference external specs or documents (for example MicroProfile specs)