Add jest matchers to check if a value matches an OpenAPI response

[greeeg]

Use what Jest documentation describes here to check if a server returns valid OpenAPI responses.

Using Supertest for example:

describe('GET /users', function() {
  it('responds with json', function() {
    return request(app)
      .get('/users')
      .set('Accept', 'application/json')
      .expect('Content-Type', /json/)
      .expect(200)
      .then(response => {
         expect(response.body).toMatchOpenAPIOperation('getPets')
      })
  });
});