Add events to rbac example

What does this MR do?

Add events RBAC resources to the values.yaml documentation

Why was this MR needed?

Starting to 16.2 gitlab-runner, kubernetes events are managed. It should be added to the doc.

What's the best way to test this MR?

1. Create a role on kubernetes without events rbac rights
2. Run a job that fails: the runner will complain about rbac issues
3. Update rbac and run the job again.

What are the relevant issue numbers?

Fixes #491 (closed)