docs: Make Testing sections more consistent

*Description*:
The following pages are missing instructions for testing/verifying without an external load balancer.

- [ ] Backend Routing
- [ ] Circuit Breakers
- [ ] Client Traffic Policy
- [ ] Connection Limit
- [ ] Direct Response
- [ ] Failover
- [ ] Fault Injection
- [ ] Global rate limit
- [ ] GRPC Routing
- [ ] HTTP Redirects
- [ ] HTTP Request Headers
- [ ] HTTP Response Headers
- [ ] HTTP Routing
- [ ] HTTP Timeouts
- [ ] HTTP URL Rewrite
- [ ] HTTPRoute Request Mirroring
- [ ] HTTPRoute Traffic Splitting
- [ ] Load Balancing
- [ ] Local Rate Limit
- [ ] Multicluster Service Routing
- [ ] Response Compression
- [ ] Response Override
- [ ] Retry
- [ ] Routing outside Kubernetes
- [ ] TCP Routing
- [ ] UDP Routing
- [ ] API Key Authentication
- [ ] Basic Authentication
- [ ] CORS
- [ ] External Authorization
- [ ] IP Allowlist/Denylist
- [ ] JWT Authentication
- [ ] JWT Claim-Based Authorization
- [ ] Envoy Patch policy
- [ ] Extension Server
- [ ] External Processing
- [ ] Wasm Extensions
- [ ] Configuration Issues

The following pages are missing instructions for testing/verifying with an external load balancer.

- [ ] Session Persistance
- [ ] Accelerating TLS Handshakes using Private Key Provider in Envoy
- [ ] Backend Mutual TLS: Gateway to Backend
- [ ] Backend TLS: Gateway to Backend (in Testing TLS Parameters section)
- [ ] OIDC Authentication
- [ ] Secure Gateways
- [ ] Using cert-manager for TLS Termination
- [ ] Deployment Mode
- [ ] Standalone Deployment Mode