GHSA-fqfg-c577-2vc3: rdiffweb's unlimited length Fullname field can lead to DoS

rdiffweb prior to 2.5.0a3 does not validate email length, allowing users to insert an email longer than 255 characters. If a user signs up with an email with a length of 1 million or more characters and logs in, withdraws, or changes their email, the server may cause denial of service due to overload.