When AHS is turned on, if we can't view application in RM page, RM page should redirect us to AHS page. For example, when you go to cluster/app/application_1, if RM no longer remember the application, we will simply get "Failed to read the application application_1", but it will be good for RM ui to smartly try to redirect to AHS ui /applicationhistory/app/application_1 to see if it's there. The redirect usage already exist for logs in nodemanager UI.
Also, when AHS is enabled, WebAppProxyServlet should redirect to AHS page on fall back of RM not remembering the app.
YARN-3975 tried to do this only when original tracking url is not set. But there are many cases, such as when app failed at launch, original tracking url will be set to point to RM page, so redirect to AHS page won't work.