Add ability to customize WebClient per connection name

When creating NamedClientMcpTransport, support ability to customize WebClient per connection name.

Current code creates the WebClient like webClientBuilderProvider.getIfAvailable(WebClient::builder):

public List<NamedClientMcpTransport> streamableHttpWebFluxClientTransports(
		McpStreamableHttpClientProperties streamableProperties,
		ObjectProvider<WebClient.Builder> webClientBuilderProvider,
		ObjectProvider<ObjectMapper> objectMapperProvider) {

	var webClientBuilderTemplate = webClientBuilderProvider.getIfAvailable(WebClient::builder);
	
    return streamableProperties.map(streamableProperty -> {
            var transport = newTransport(webClientBuilderTemplate, streamableProperty)
            streamableHttpTransports.add(new NamedClientMcpTransport(transport))
           }).toList();
}

Please make the code read something like webClientFactory.create(connectionName, WebClient::builder):

public List<NamedClientMcpTransport> streamableHttpWebFluxClientTransports(
		McpStreamableHttpClientProperties streamableProperties,
		WebClientFactory webClientFactory,
		ObjectProvider<ObjectMapper> objectMapperProvider) {
	
    return streamableProperties.map(streamableProperty -> {
            var connectionName = streamableProperty.connectionName()
			var webClientBuilder = webClientFactory.create(connectionName, WebClient::builder);
            var transport = newTransport(webClientBuilderTemplate, streamableProperty)
            streamableHttpTransports.add(new NamedClientMcpTransport(transport))
           }).toList();
}

Context
This will allow WebClient and underlying http client to be much more easily customized on a per connectionName basis.

Start in auto-configurations/mcp/spring-ai-autoconfigure-mcp-client-webflux/src/main/java/org/springframework/ai/mcp/client/webflux/autoconfigure/StreamableHttpWebFluxTransportAutoConfiguration.java, focusing on streamableHttpWebFluxClientTransports and newTransport. Trace how each streamable property supplies its connection name and how the WebClient.Builder is obtained. Done means WebClient customization can be selected independently for each connection name while existing NamedClientMcpTransport creation continues to work.