Routes metadata keys are treated as case-insensitive when retrieved

Describe the bug
cloudgatewayVersion = '4.3.0'
When retrieving route metadata in Spring Cloud Gateway, the keys appear to be matched in a case-insensitive manner. This causes unexpected results.

Sample
sample config:-

spring:
  application:
    name: gw
  cloud:
    gateway:
      default-filters:
      routes:
       - id: route1
         order: 1
         uri: http://127.0.0.1:1010/
         metadata:
            customMetaData: abc

sample code:-

Route route = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR);
Map<String, Object> metaData = route.getMetadata();
metaData.get("customMetaData"). // returns null

The issue appears to be with GatewayServerWebfluxPropertiesMigrationListener. When using the new prefix, it works as expected : spring.cloud.gateway.server.webflux

Start by locating GatewayServerWebfluxPropertiesMigrationListener and trace how route metadata from the old configuration prefix is converted into Route metadata. Reproduce the sample configuration and compare retrieval of customMetaData with the new spring.cloud.gateway.server.webflux prefix; done means metadata keys retain their case under the affected configuration path.