NIM: Incorrect variable names, OIDC

[mjang]

Describe the bug

In this section, https://docs.nginx.com/nginx-instance-manager/admin-guide/authentication/oidc/microsoft-entra-setup/#configure-nginx-plus

step 3, there's a reference to client_key, tenant_key, and client_secret

The names have changed in the referenced file, and the doc should change accordingly.

To reproduce

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Expected behavior

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Your environment

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• Target deployment platform

Additional context

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[mjang]

As reported by @fabriziofiorucci

[mjang]

Replaced by #243