Maps an incoming URI to a new target URI. The new URI can be prefixed with "redirect:", "permanent:" or "forward:" to trigger
either a temporary redirect, a permanent redirect or a forward respectively. For redirects the URI can be
absolute or relative within the web application (the context path is added automatically). If the mapping does
not apply to the input URI this method returns null.
uri - a relative URI containing only the path and query components.
The path is relative to the magnolia servlet mapping; context path is already stripped.
Validate necessary info to check VirtualUriMapping is valid.