[Test] Add Spring Cloud Gateway 4.3.3 and 5.0.0 to gateway scenario

[Siman-hub]

Summary

This PR adds Spring Cloud Gateway 4.3.3 and 5.0.0 to the gateway-4.x-scenario test matrix.

Compatibility Analysis

I verified source-level compatibility of NettyRoutingFilter in Gateway 4.3.3 and 5.0.0 against the existing v412x plugin.

• Structure change: Gateway introduces getHttpClientMono, which is invoked by the main filter flow.
• Safety check: In both versions, the implementation remains eager:

// org.springframework.cloud.gateway.filter.NettyRoutingFilter (v4.3.3)
protected Mono<HttpClient> getHttpClientMono(Route route, ServerWebExchange exchange) {
    return Mono.just(getHttpClient(route, exchange));
}

• Conclusion: Since Mono.just is evaluated immediately on the calling thread, getHttpClient(...) (which SkyWalking instruments) is still executed synchronously during request handling. Execution order and context propagation remain unchanged, so the existing plugin continues to work as intended for both 4.3.3 and 5.0.0.

Verification

• Validated source compatibility (NettyRoutingFilter structure).
• Validated binary compatibility (Plugin compiles against 4.3.3 and 5.0.0).
• Runtime verification delegated to CI (Local Windows environment limitations prevented full Docker scenario execution).