feat(OAS 3-requestBody): Support for OAS 3 requestBody as customValue

[osvaldo2627]

Allows the specification of a requestBody as a customValue for [POST, INT, PUT] methods.
For example:

  "/user": {
    "post": {
      "200": {
          "requestBody": {
              "name": "John Doe",
              "age": 15
          },
          "response": {
              "name": "John Doe"
          }
      }
    }
  }

I know that parsing parameters relays on the sway implementation. But "requestBody" from OAS 3 is still not supported and for OAS-3.X is not a parameter anymore.
What do you think about having this here?