oas-validation plugin

There is a new plugin available since 3.1: oas-validation (https://docs.konghq.com/hub/kong-inc/oas-validation/)

I would be interested how to integrate that one into the spec file for creating a decK configuration:

Currently, I'm injecting the spec file in a CICD pipeline with the help of an ENV variable:

```
- name: oas-validation
config:
api_spec: ${{ env "DECK_OAS_SPEC_NOC_HTTPBIN" }}
verbose_response: true
```

Sample idea:
```
openapi: 3.0.1
info:
version: '1.0-oas3'
title: httpbin
description: An unofficial OpenAPI definition for [httpbin.org](https://httpbin.org).

servers:
- url: https://httpbin.org

tags:
- name: auth
description: Operations for testing various authentication types
- name: HTTP methods
description: Operations for testing different HTTP methods
- name: Status codes
description: Return the specified HTTP status code, or a random status code if more than one are given

x-kong-plugin-oas-validation:
enabled: true
```

Start with the oas-validation plugin documentation linked in the issue and the decK configuration example shown in its body. Compare the current ENV-based api_spec setup with the proposed x-kong-plugin-oas-validation OpenAPI extension. Done means establishing and documenting a supported integration path, with any required configuration behavior verified.

Written by the indexing model from the issue text.