ref(server): Use async/await in all endpoints

[jan-auer]

Moves all endpoints and most HTTP utilities to async/await. This is to prepare
upgrading the web framework.

#skip-changelog

[jan-auer]

The failing integration test shows that error reporting has changed with my refactored store endpoints. Since the endpoints now return an error, actix_web::pipeline logs a duplicate error message (but without the causes). This is undesirable since it would create noise in Sentry.

See the following excerpt. The first line is our manual log, the other two are now added by actix_web:

[relay_server::endpoints::common] ERROR: error handling request: failed to queue envelope
  caused by: envelope buffer capacity exceeded
[actix_web::pipeline] ERROR: Error occurred during request handling, status: 503 Service Unavailable failed to queue envelope
[actix_web::pipeline] DEBUG: QueueFailed(BufferError)

I'm looking into a quick fix. It's useful to return an error, but on the other hand we want clean error logs and reports.

Update: Like in the past, the only workaround is to convert BadStoreRequest before it hits the actix-web pipeline. Since we already needed specific boilerplate to create actix-web handlers, I decided to create a simple wrapper functions that converts the error and creates a compat future.

[olksdr]

lgtm 🚀

[jjbayer]

Did not look at the details but in general this looks good to me! Great improvement in code readability.

[jjbayer]

If self.chunk() returns an error, this function will silently fail. Is that the same behavior as we had before?

[jan-auer]

Yes, we want to consume until there's an error and then bail.

[iker-barriocanal]

So much simpler! 🙌