[Form] Not possible to add additional fields through form action configuration

When I configure a form action in the Container component, the "addfields.jsp" (or "addfields.html") script is not invoked.

Back in the "old" days, we had in the FormsHelper the startForm(request, response) function, that would at the very end of setting up the form, execute:
` String actionType = (String)properties.get("actionType", "");
if(actionType.length() > 0) {
runAction(actionType, "addfields", formResource, request, response);
}`

This, however, is missing in the new Container component. Therefore, we are unable to add custom fields (or other HTML) to the forms that we use.

Start with the Container component's form action configuration and compare its form setup with the older FormsHelper.startForm(request, response) flow described here. Trace whether addfields.jsp or addfields.html is invoked for the configured action, and consider the work complete when custom fields or other HTML can be added to the rendered form.

Written by the indexing model from the issue text.