Add OpenAPI U/I integration [3.x]

[tjquinno]

Resolves #4883

SmallRye offers a mostly-static content solution for presenting essentially the Swagger U/I.

This PR creates a new integration--helidon-integrations-openapi-ui--which layers on the SmallRye code, customizing the main page dynamically with some Helidon-specific content (logo, title, links) and serving the U/I at at /openapi/ui (by default) and, using content negotiation, also at /openapi.

SE developers add a build-time dependency and then create an OpenApiUi.Builder instance and add it to the OpenAPISupport.Builder if they want to customize the U/I behavior. Or, they can just let OpenAPISupport.Builder automatically create a U/I using default settings. They can use config for a few settings as well.

MP developers add a runtime dependency and use config as needed to tailor the behavior.

Changes to helidon-openapi

• Defines some new U/I-related interfaces (OpenApiUiFactory and OpenApiUi) and contains no-op implementations.
• OpenAPISupport:
  • Uses service loading to obtain the correct factory and get the correct OpenApiUi.Builder impl
  • Invokes the OpenApiUi update method so it can add its own routing. (none for the no-op impl) The developer's code does not explicitly register the U/I service.
  • delegates to the OpenApiUi instance upon receiving a request at /openapi so it can handle requests for text/* content.
• Some new tests

New helidon-integrations-openapi-ui

• Provides its OpenApiUiFactory impl and contains a full-featured OpenApiUi impl which:
  • Redirects HTML requests to /openapi and /openapi/ui to return a dynamically-computed index.html (from SmallRye) which contains JavaScript which retrieves the OpenAPI document and then runs the browser U/I)
  • Adds routing for static content, some from Helidon, some from SmallRye, used by the U/I.
• Some Helidon-specific static content for the U/I page.
• Tests

MP QuickStart examples

• Added an MP OpenAPI annotation to add some information so the U/I is nicer if someone were to add the Helidon OpenAPI U/I dependency to the MP QuickStart pom manually.

Docs

• Extensive additions to describe adding the U/I dependency and using the builder or config to tailor the behavior.
• Removed se/openapi.adoc which was moved to se/openapi/openapi.adoc in a previous PR but I accidentally left the old file in place.
• Fixed an unrelated typo in the OpenAPI generator doc.

[ljamen]

I didn't call them out individually, but perhaps we should stick to UI (vs U/I) throughout the docs? Is there a way to find/replace? The only other issue I had was with the logo.svg file. It wasn't displaying for me -- or at least it didn't look like it was?