[New Docs PR] - Helidon MP OpenAPI #4209

[dalexandrov]

Resolves #4209

[tjquinno]

General notes:

1. I had created PR Fix config doc annotations for OpenAPI builder #4419 with pom.xml and .java and generated docs/shared/config/*.adoc file changes in it earlier. I've continued to fine-tune those changes. Following up on Tomas's comment in our recent meeting, let's use those changes and reserve this PR for the hand-written .adoc content. (We could try to merge that PR's changes into this one but there's no real need to do so and it would just create unneeded work for someone.)
2. I think there will be considerable shared content between the updated SE and MP OpenAPI .adoc pages. It probably makes sense to continue with the changes to docs/mp/openapi/01_openapi.adoc as drafted (and commented on) here with the understanding that we will want to refactor the common content out into a separate file that this .adoc and the SE one will both include, rather than duplicating the content in two places.

[dalexandrov]

1. I hope did it right. Would you please check.
2. I think, a good idea will be to first finish this doc, to have it as a reference, and then, as we edit the SE doc, to extract the common parts and edit both of them. I hope you like this idea :)

[tjquinno]

Excellent progress. A few minor edits left.

[tjquinno]

So close! See especially the comment about the links to the MP OpenAPI doc.

And since you'll be updating the file, there's one other much more minor note.