E2E test for Group-level Audit Event Streaming

Summary

Create a group.
Set up a server to receive streamed events.
Use the UI to configure the group to stream events to that server.
Perform an action that triggers a group-level audit event (e.g., create a group).
Perform an action that triggers an event that is only available via streaming (e.g., delete merge request).
Perform an action that triggers a project-level audit event (e.g., create a project).
Perform an action that triggers an instance-level audit event (e.g., add a user).
Query the streaming server to confirm that all events were received, with the correct verification token (depends on gitlab-org/gitlab!118513 (merged)), except the instance-level event.