6.x http response cleanup (#8040)

* add Client\Http\Response method changes

* fix RST syntax problem

Author: LordSimal

en/appendices/6-0-migration-guide.rst

@@ -82,8 +82,10 @@ Datasource
 Http
 ----
 
-- Using `$request->getParam('?')` to get the query params is no longer possible.
-  Use `$request->getQueryParams()` instead.
+- Using ``$request->getParam('?')`` to get the query params is no longer possible.
+  Use ``$request->getQueryParams()`` instead.
+- The methods ``_getCookies()``, ``_getJson()``, ``_getXml()``, ``_getHeaders()``
+  and ``_getBody()`` have been removed. Use/Overwrite their non-prefixed public alternative instead.
 
 ORM
 ---