Ensure Sentry ingestion does not block PR merges

[mydea]

Today, most of our E2E tests ensure we send payloads to Sentry. This means we wait for stuff to be ingested by Sentry, which also means that if that is delayed or broken the tests failed, meaning we cannot merge PRs.

We do not want to be blocked like this. So to fix this, I propose that we:

1. Create 1 or 2 new E2E tests that literally only test that we can send stuff to Sentry. We make this tests non-blocking, like the flaky test detector - meaning even if that fails you can merge a PR. There is no need to test this for every framework/SDK, it should be enough to maybe have one browser, one node, maybe next.js there.
2. All other E2E tests stop testing that we send to sentry, and instead only check payloads etc. via the event proxy.