Add webapi integration testing tool

[oskardudycz]

Add WebApi integration tool like in the testing projections article. It should be:

• using given/when/then pattern
• take events in given and supertest request in when,
• Then can tests events like command handling tests, but also should allow to doqueries etc,
  It should enable testing idempotency and optimistic concurrency, so running requests twice.
• in the future, it could be testing OTel spans as Martin Thwaites shown in his talks,
• This is not perfect with an in-memory event store but should be fine for business logic and integration tests in the ports/adapters style.

[oskardudycz]

Fixed by #25.