Feature Request: Add proxy_intercept_errors to nginx plugin

[Jannik-Hm]

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Describe the solution you'd like
As it is already possible to create custom error pages, it would be a nice addition to add proxy_intercept_errors as a toggle, to override downstream error responses.

For example, I currently have nginx on opnsense as my central reverse proxy. It distributes to all other servers / services.
One of those services is a kubernetes cluster with traefik for handling traffic. When traefik now responds with a 403 error code, nginx just forwards the traefik error page instead of serving the custom nginx one.