Add support for additionalProperties in inline object

[isc-tstolker]

After fixing #32 I found that there is still a case not addressed.
For some reason, the following inline response is not flattened, causing the generator to not genereate anything for a 200 response:

    "/internal/network/v1/diagnostics/peers":{
      "get":{
        "tags":[
          "diagnostics"
        ],
        "summary":"Gets diagnostic information about the node's peers",
        "operationId":"getPeerDiagnostics",
        "responses":{
          "200":{
            "description":"Successfully retrieved peers diagnostics",
            "content":{
              "application/json":{
                "schema":{
                  "type":"object",
                  "additionalProperties":{
                    "$ref":"#/components/schemas/PeerDiagnostics"
                  }
                }
              }
            }
          },
          "default":{
            "$ref":"../common/error_response.yaml"
          }
        }
      }
    },