Downgrade rampart version
Downgrade rampart version

Related to wso2/product-ei#2398.
Change rampart version to v28 to maintain uniform version

milindaperera/product-ei,wso2/product-ei,milindaperera/product-ei,milindaperera/product-ei,wso2/product-ei,wso2/product-ei,wso2/product-ei,milindaperera/product-ei,wso2/product-ei,milindaperera/product-ei