Updating example for cluster-resource

[agm650]

Description

Updating example of sensuctl cluster-role create to use plurals for verbs & resources

Motivation and Context

Reflecting changes in sensu-go#4141 in documentation. This is linked to the pull request sensu-go#4635

Review Instructions

Signed-off-by: Luc Dandoy [email protected]

[hillaryfraley]

@agm650 thank you for opening this PR to sync the docs with your code change! When this change is added to a specific release, I'll get your update into the correct set of docs. Thank you for taking the time to make the Sensu docs better!