networking: add pathTemplate match type to StringMatch

[AntonioMorales97]

Description

Add a new pathTemplate oneof variant to StringMatch to support URI template path matching in VirtualService HTTPMatchRequest.uri.

This allows matching patterns like /users/{*}/orders without resorting to regex:

apiVersion: networking.istio.io/v1
kind: VirtualService
metadata:
  name: example
spec:
  hosts:
  - example.com
  http:
  - match:
    - uri:
        pathTemplate: "/users/{*}/orders"
    route:
    - destination:
        host: orders-service

• {*} matches exactly one path segment
• {**} matches one or more path segments (must be the last operator)

Backed by Envoy's UriTemplateMatchConfig extension, the same mechanism already used for AuthorizationPolicy path matching.

Motivation

• Consistency: AuthorizationPolicy already supports {*}/{**} path templates (#47306); VirtualService should too
• Simplicity: more readable and less error-prone than equivalent regex for REST API patterns
• Performance: avoids regex evaluation overhead

Related

• Fixes Support {*} / {**} path template operators in VirtualService URI matching istio#59533
• #47306 — added {*}/{**} to AuthorizationPolicy

The implementation in istio/istio is submitted as a dependent PR and will be linked once this merges.

[istio-policy-bot]

🤔 🐛 You appear to be fixing a bug in Go code, yet your PR doesn't include updates to any test files. Did you forget to add a test?

Courtesy of your friendly test nag.

[istio-policy-bot]

😊 Welcome @AntonioMorales97! This is either your first contribution to the Istio api repo, or it's been
a while since you've been here.

You can learn more about the Istio working groups, Code of Conduct, and contribution guidelines
by referring to Contributing to Istio.

Thanks for contributing!

Courtesy of your friendly welcome wagon.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: AntonioMorales97 / name: Antonio Morales (fbdb857)

[istio-testing]

Hi @AntonioMorales97. Thanks for your PR.

I'm waiting for a istio member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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