Set maximum payload size to 10MB

[fuzzypixelz]

This increases the maximum payload size for the entire Actix app to 10MB.

We've hit the size limit while publishing Eclipse Zenoh 1.0.0-alpha.1:

error: failed to publish to registry at http://localhost:7878
  Caused by:
    failed to get a 200 OK response, got 413
    headers:
        HTTP/1.1 413 Payload Too Large
        content-length: 29
        content-type: text/plain; charset=utf-8
        date: Thu, 20 Jun 2024 13:51:03 GMT
        
    body:
    A payload reached size limit.

For reference crates.io has a maximum upload size of 10MB.

[diogomatsubara]

@onelson could you take a look at this PR?