Doc: MP/SE content for Open API

[ljamen]

Environment Details

• Helidon Version: 2.0.x
• Helidon SE and Helidon MP

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Problem Description

We need to provide additional content for both the SE and MP versions of Open API per Dmitry's doc epic.
Specifically we need to:

Reflect Helidon 2.0 changes (if any)
Cover more use cases.

Steps to reproduce

Existing doc can be found here:
https://helidon.io/docs/v2/#/mp/openapi/01_openapi

https://helidon.io/docs/v2/#/se/openapi/01_openapi

[tjquinno]

There are no changes required to the Helidon 2.0 doc for OpenAPI in SE or MP.

We could add more use cases, but that would greatly expand the length and go against our goal of keeping the one-pagers short and sweet. If we really feel we need to add further use cases, we might consider adding a guide rather than expanding the current one-pager.