Allow redirection to a file path

Problem/Motivation

Allow the user to add a redirection rule that redirects the page to a file placed in the server.
Right now, the redirection rules that redirects to a file are not allowed. But, it is also possible that the name or the path of a file cahnges, so makes sense to allow also to redirect a page to a file path.

Proposed resolution

For fixing that, the validation of the redirection rule should also take in account that the path introduced can be a file placed in the server.