[4.x] Allow SE users work with OpenApiFeature instead of SeOpenApiFeature

[tjquinno]

Resolves #7041

Previously, SE developers would directly use SeOpenApiFeature in nima/openapi. We want them to not use "SE" anything.

That class was the only one in nima/openapi. This PR:

1. Moves SeOpenApiFeature to helidon/openapi and makes it non-public.
2. Adds OpenApiFeature#builder() which returns an OpenApiFeature.Builder which actually returns a builder for SeOpenApiFeature. Going forward SE developers will use OpenApiFeature.builder() (instead of SeOpenApiFeature.builder()) to prepare the feature so they can add it to their routing.
3. Moves tests and supporting resource files from nima/openapi to microprofile/openapi. Those tests and resources refer to SmallRye OpenAPI elements. We continue to rely on SmallRye for our MP OpenAPI implementation but we will not for SE. So those tests could not move to helidon/openapi or we'd have to add the SmallRye dependency to that component.
4. Updates the SE quickstart app to use the new OpenApiFeature#builder method.
5. Unplugs nima/openapi from the nima module.

This PR does not address doc changes; we have a separate issue to address the OpenAPI doc.

Also, this PR leaves some of the transplanted tests commented out (due to other pressing tasks!); they were originally written to work with SE and need to be adjusted to work with MP now that they are in MP OpenAPI now.

@romain-grecourt I did not see any references to SeOpenApiFeature in the archetypes directory but I've tagged you as a reviewer just so you can double-check.