Add documentation for Request Routing in Kmesh (L7 capability)

[AkarshSahlot]

This PR contributes documentation for Issue #600, expanding the official Kmesh developer documentation with an example of Layer 7 (L7) request routing.
Included in this PR:
• A new file: docs/l7/request-routing.md
• Introduction and overview of L7 request routing in Kmesh
• Step-by-step example using Gateway API and httpbin-v1/httpbin-v2 services
• YAML config for HTTPRoute with multiple match rules
• Verification steps using curl from the sleep pod
• Notes on prerequisites and known limitations
• Related references for Kmesh and Istio documentation
The goal is to help users understand and experiment with L7 routing based on path prefixes, and to build a foundation for future docs on additional L7 features (timeouts, traffic shifting, etc.).
Please let me know if the structure or example should be adjusted. Happy to follow up with more L7 feature docs in subsequent PRs.
Fixes #600

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[gemini-code-assist]

Summary of Changes

Hello @AkarshSahlot, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

I've added comprehensive documentation for Layer 7 (L7) request routing in Kmesh. This new guide focuses on path-based routing, providing a clear, step-by-step example using Gateway API and httpbin services. The goal is to help users understand and implement L7 routing, laying the groundwork for future documentation on advanced L7 features.

Highlights

• New Documentation File: A new file, docs/l7/request-routing.md, has been added to the Kmesh developer documentation.
• L7 Request Routing Overview: The document provides an introduction and overview of Layer 7 (L7) request routing in Kmesh.
• Detailed Example for Path-Based Routing: A step-by-step example demonstrates path-based routing, showing how to direct traffic to different httpbin service versions based on URL path prefixes (/v1 and /v2).
• Gateway API Configuration Example: The documentation includes the YAML configuration for an HTTPRoute resource, illustrating how to set up multiple match rules for path-based routing using Gateway API.
• Verification Steps: Clear instructions are provided for verifying the routing configuration, including curl commands to be executed from a sleep pod.
• Prerequisites and Limitations: The document outlines necessary prerequisites for setting up L7 routing and notes known limitations, such as header-based and regex path matching requiring further validation.

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[gemini-code-assist]

Code Review

This pull request adds valuable documentation for L7 request routing in Kmesh. The example is clear and helpful. I've found a critical issue in the provided YAML configuration that would prevent it from working, and I've also suggested some changes to make the example self-contained and easier for users to follow. My feedback focuses on ensuring the documentation is accurate and immediately usable.

[gemini-code-assist]

The YAML for the HTTPRoute is invalid. The field meta should be metadata:. With the current configuration, kubectl apply -f http-route.yaml will fail because the resource specification is malformed.

Suggested change

	meta
	metadata:

[gemini-code-assist]

The example relies on an example-gateway which is not defined in this document. This makes the example incomplete and hard for users to follow. For demonstrating mesh request routing, it's more common and clearer to attach the HTTPRoute to a Service.

I suggest the following changes to make the example self-contained:

1. In Step 1, create a virtual httpbin service that will act as the parent for the route. You can add instructions to create a file (e.g., httpbin-service.yaml) with the following content and apply it:

   apiVersion: v1
   kind: Service
   metadata:
     name: httpbin
     namespace: example
   spec:
     ports:
     - port: 8000
       name: http
     selector:
       # This service has no pods, it's just a handle for the HTTPRoute.
       app: non-existent

2. In Step 2, update the HTTPRoute to reference this new service as its parent, as suggested below.

Suggested change

	parentRefs:
	- name: example-gateway
	parentRefs:
	- name: httpbin
	kind: Service
	port: 8000

[gemini-code-assist]

Following the suggestion to use a Service as the parentRef for the HTTPRoute, this line assuming an example-gateway is no longer necessary and could cause confusion. It should be removed.

[YaoZengzeng]

Looks like we already have this doc, ref: https://kmesh.net/docs/application-layer/try-request-routing

[AkarshSahlot]

Thank you for pointing that out! Yes, I noticed the existing documentation and my PR focuses on testing or demonstrating the process specifically on the macOS platform. I wanted to share my experience to help macOS users better follow the steps.

[hzxuzhonghu]

@AkarshSahlot If this is for macos, i am not sure kmesh works. If it can work on mac os. Can you please update the install guide rather than for each task