Configuration attribute to disable CORS processing when response already has CORS headers

Is your feature request related to a problem? Please describe.
When proxied services already set CORS headers, I end up with double headers definition and CORS error in web browser.

All solutions that I found so far to disable CORS actually just allow any origin for any kind of requests, which sets headers and lead to the error I face.

Describe the solution you'd like
I'd like a configuration option to disable completely corsProcessor in AbstractHandlerMapping when a response already carries Access-Control-Allow-* headers (not override nor add header with the same name)

Describe alternatives you've considered
First solution is to disable CORS in downstream services. This works for resource-servers that I code but sometimes, I just can't disable CORS (like when proxying a Keycloak server). Also, web-applications can't use the resource-servers directly anymore.

Other solution I found is to explicitely setResponseHeader in a filter. This de-duplicates headers but resource-servers CORS headers are lost (as explained earlier, I'd prefer to use those original headers only):

	@Bean
	public RouteLocator myRoutes(RouteLocatorBuilder builder, Function<GatewayFilterSpec, UriSpec> brutalCorsFilters) {
		return builder.routes().route(p -> p.path("/users/**").filters(brutalCorsFilters).uri("https://localhost:9443"))
				.route(p -> p.path("/greet/**").filters(brutalCorsFilters).uri("https://localhost:9445"))
				.route(p -> p.path("/realms/**").filters(brutalCorsFilters).uri("https://localhost:8443"))
				.build();
	}

	@Bean
	Function<GatewayFilterSpec, UriSpec> brutalCorsFilters() {
		// use something more restrictive in production
		return f -> f
				.setResponseHeader("Access-Control-Allow-Origin", "*")
				.setResponseHeader("Access-Control-Allow-Methods", "*")
				.setResponseHeader("Access-Control-Allow-headers", "*")
				.setResponseHeader("Access-Control-Expose-Headers", "*");
	}

with this properties:

spring.cloud.gateway.globalcors.add-to-simple-url-handler-mapping=true
spring.cloud.gateway.globalcors.corsConfigurations.[/**].allowed-origins=*
spring.cloud.gateway.globalcors.corsConfigurations.[/**].allowed-headers=*
spring.cloud.gateway.globalcors.corsConfigurations.[/**].allowed-methods=*
spring.cloud.gateway.globalcors.corsConfigurations.[/**].exposed-headers=*

Start with Spring's AbstractHandlerMapping and its corsProcessor, then trace the spring.cloud.gateway.globalcors configuration described in the issue. Determine where a configuration option could disable processing when the response already contains Access-Control-Allow-* headers. Done means upstream CORS headers remain unchanged and the gateway does not add duplicate headers.