Response/error codes aren't outlined

### Which section?

SDKs

### Page URL

https://develop.sentry.dev/sdk/data-model/envelopes/

### Description

This page outlines how to call the `api/{project}/envelope` endpoint, but never outlines what HTTP response codes should be expected, and in what scenarios.

### Suggested Solution

Provide HTTP response/error codes, and situations where they would be relevant