Add option to conditional proxy in routingRules.

[comfuture]

Describe the feature

I would like to request support for conditional proxy in routingRules.

This feature would allow, for example, serving different versions of the same entity (e.g., application/ld+json) based on the Accept header. Instead of branching based on headers in each eventHandler, this would enable handling such branching collectively in routingRules.

Additionally, if a server route could respond conditionally to routes that already exist in Nuxt's pages, it would be extremely useful for building services like ActivityPub and similar protocols.

Additional information

• Would you be willing to help implement this feature?