Verify Crash Envelope iOS has been sent in UI tests

[krystofwoldrich]

Description

Current Critical UI tests use production Sentry DSN and do not check if the crash envelope left the device.

We would add a mock Sentry Relay to assert that the app recovers (cover by current tests) and also sends a crash report.

• Java PR: test(critical): Add Mock Relay to verify crash envelope sentry-java#3811

[brustolin]

We do have a Swift Vapor server where we test HTTP requests; you probably can use it too.

[philipphofmann]

The test server is here https://github.com/getsentry/sentry-cocoa/tree/main/test-server.