4.x Review/update OpenAPI docs and examples now that OpenAPI is a server feature and added automatically

[tjquinno]

Environment Details

• Helidon Version: 4.0.0
• Helidon SE or Helidon MP SE
• JDK version:
• OS:
• Docker version (if applicable):

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Helidon OpenAPI was turned into a server feature late in 4.0.0, introducing changes in behavior. For example, Helidon now adds OpenAPI automatically if it is on the class path with no need for the developer to explicitly add it to the server or routing as was required in 3.x.

• Review/update OpenAPI documentation
• Review/update OpenAPI-related examples