Add golang shim for comms with EPP

[sjberman]

Problem: In order for NGINX to get the endpoint of the AI workload from the EndpointPicker, it needs to send a gRPC request using the proper protobuf protocol.

Solution: A simple Go server is injected as an additional container when the inference extension feature is enabled, that will listen for a request from our (upcoming) NJS module, and forward to the configured EPP to get a response in a header.

Testing: Manually sent a request to the Golang app and received the endpoint header in the response.

Closes #3837

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[Copilot]

Pull Request Overview

This PR introduces a Go-based HTTP shim server that enables NGINX to communicate with the Gateway API Inference Extension Endpoint Picker via gRPC. The implementation adds new command-line functionality and container injection capabilities to support inference workload routing.

• Adds an endpoint-picker command to the gateway binary that runs an HTTP server
• Introduces container injection logic for the inference extension feature
• Implements gRPC client functionality to communicate with the External Processing Protocol (EPP)

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
cmd/gateway/endpoint_picker.go	Core HTTP server implementation for EPP communication
cmd/gateway/endpoint_picker_test.go	Comprehensive test suite for the endpoint picker functionality
cmd/gateway/commands.go	Adds the new endpoint-picker command to the CLI
cmd/gateway/main.go	Registers the endpoint-picker command in the root command
internal/controller/provisioner/objects.go	Implements container injection logic for inference extension
internal/controller/provisioner/objects_test.go	Tests for container injection functionality
internal/controller/provisioner/provisioner.go	Adds InferenceExtension configuration field
internal/controller/manager.go	Passes InferenceExtension config to provisioner
go.mod	Adds required gRPC and protobuf dependencies

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[bjee19]

there are a couple of nits related to spacing / new lines before return statements, but it seems so common perhaps thats no longer in our style guidelines, but elsewise lgtm

[bjee19]

Actually as a question, I thought #3841 says that the communication between the go app and the EPP will use TLS. But here it sends a grpc request. Am i missing something or has some stuff been changed?

Or does gRPC satisfy the tls requirements already? Or are these things not mutually exclusive?

[sjberman]

@bjee19 Not mutually exclusive, right now this sends an insecure gRPC request, that we'll need to secure with a certificate/key.