improvement: add e2e test for relay and gateway

[fangpenlin]

Description 📣

ref: https://linear.app/infisical/issue/PLATFRM-128/pick-one-vertical-slice-to-add-tests-with-the-new-e2e-infra

Type ✨

• Bug fix
• New feature
• Improvement
• Breaking change
• Documentation

Tests 🛠️

# Here's some code block to paste some code snippets

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• I have read the contributing guide, agreed and acknowledged the code of conduct. 📝

[greptile-apps]

Greptile Summary

This PR adds comprehensive end-to-end test infrastructure for relay and gateway functionality. The changes include three new test cases covering relay registration, gateway registration, and relay-gateway-PAM connectivity with both Kubernetes and Redis resources.

Key improvements:

• Refactored CLI command structure to export RootCmd and support dynamic stdout/stderr writers, enabling better testability
• Implemented flexible test execution modes (subprocess and functionCall) with proper state management
• Added robust wait helpers (WaitFor, WaitForStderr) with proper command lifecycle checks
• Updated logger utilities to support configurable output writers for test output capture
• Comprehensive documentation in README covering setup, configuration, and troubleshooting

The tests properly use testcontainers to spin up Redis and mock HTTP servers, validate heartbeats, and verify connectivity through the relay-gateway architecture.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The changes are well-structured test infrastructure additions with proper error handling, cleanup mechanisms, and no security concerns. All refactorings are safe and improve testability without affecting production behavior.
• No files require special attention

Important Files Changed

Filename	Overview
e2e/relay/relay_test.go	Added comprehensive e2e tests for relay registration, gateway registration, and relay-gateway-PAM connectivity (Kubernetes and Redis). All tests follow good patterns.
e2e/relay/helpers_test.go	Refactored test helpers to support both subprocess and functionCall run methods with improved state management and proper cleanup. Good error handling.
e2e/README.md	Comprehensive documentation covering test setup, configuration, and troubleshooting. Well-structured and helpful for developers.
packages/cmd/root.go	Renamed rootCmd to RootCmd for export, added dynamic stdout/stderr writers for testability, and extracted GetLoggerConfig function. Enables better testing.
packages/util/log.go	Added configurable writer functions and new helper functions for stdout/stderr to support test output redirection. Good abstraction.

[akhilmhdh]

Application testing it. Readme looks amazing

[akhilmhdh]

generate-code seems a misleading - may be like openapi-spec