Fix helm values in identity overview

[giorgionaps]

https://docs.camunda.io/docs/self-managed/components/orchestration-cluster/identity/overview/#assign-users-clients-groups-or-mapping-rules-to-roles-via-configuration helm code block is incorrect and duplicated option 3 helm code block
reported in slack https://camunda.slack.com/archives/C026U8GBNSW/p1773904416875609