Spike: Create a custom Sequence in JSLB4

[hacksparrow]

Follow up task for #1978.

Acceptance criteria

a. Should be created as a class
b. Demonstrate usage with JSLB4 Application class

[bajtos]

Renamed the story to "Spike: Create a custom Sequence in JSLB4".

I think it's important to change the default request processing in the new Sequence class, otherwise there is no point in having a custom sequence IMO. To keep this simple, I am proposing to add a minimal request logging.

class MySequence {
  // ...

  async handle(context: RequestContext) {
    try {
      const {request, response} = context;
      const route = this.findRoute(request);
      const args = await this.parseParams(request, route);
      const result = await this.invoke(route, args);
      this.send(response, result);
    } catch (error) {
      this.reject(context, error);
    }

    // Example log:
    //   GET /products 200 OK
    console.log(
      request.method,
      request.url,
      response.statusCode,
      response.statusMessage,
    );
  }

[hacksparrow]

Closing as per the decision taken in #2567.