Docs: example ClusterExtension is missing lease verbs

[trgeiger]

This section of our docs on deriving the provided ServiceAccount permissions for a ClusterExtension shows that ArgoCD requires verbs for "lease" in "coordination.k8s.io." However, our example in config/examples is missing these permissions.

[rashmi43]

/assign rashmi43

[rashmi43]

my fork was a mess, force rebased it to master and created a new PR