E2E: add Outbox processing middleware

[s373r]

Context

Outbox messages are used to communicate between different systems. Their processing occurs asynchronously.

In other words, e.g. after creating a dataset, we need to additionally create sleep()'s in our tests to ensure that all messages are completed processing.

This workaround creates instability and delays test execution time.

Expectations

It is required to implement middleware that, after changing HTTP requests (POST, PUT), processes all accumulated messages and waits for the end of this process.

In case it is a POST GQL API query, execute only if it is a mutation.