Update references for RestTemplateCustomizer and RestTemplateBuilder classes in documentation

Starting from Spring Boot 4, the RestTemplateBuilder and RestTemplateBuilder classes have been moved from the org.springframework.boot.web.client package to the org.springframework.boot.restclient package

Signed-off-by: Antoine Rey <antoine.rey@free.fr>

Author: arey

documentation/spring-boot-docs/src/docs/antora/modules/how-to/pages/http-clients.adoc

@@ -9,7 +9,7 @@ This section answers questions related to using them.
 [[howto.http-clients.rest-template-proxy-configuration]]
 == Configure RestTemplate to Use a Proxy
 
-As described in xref:reference:io/rest-client.adoc#io.rest-client.resttemplate.customization[RestTemplate Customization], you can use a javadoc:org.springframework.boot.web.client.RestTemplateCustomizer[] with javadoc:org.springframework.boot.web.client.RestTemplateBuilder[] to build a customized javadoc:org.springframework.web.client.RestTemplate[].
+As described in xref:reference:io/rest-client.adoc#io.rest-client.resttemplate.customization[RestTemplate Customization], you can use a javadoc:org.springframework.boot.restclient.RestTemplateCustomizer[] with javadoc:org.springframework.boot.restclient.RestTemplateBuilder[] to build a customized javadoc:org.springframework.web.client.RestTemplate[].
 This is the recommended approach for creating a javadoc:org.springframework.web.client.RestTemplate[] configured to use a proxy.
 
 The exact details of the proxy configuration depend on the underlying client request factory that is being used.