Support redirects for trailing slashes

[andreas-haller]

https://www.netcentric.biz/de -> works
https://www.netcentric.biz/de/ -> 404

This is because EdgeDelivery serves the document called de for the first and the document de/index for the second. To fix this behaviour we could

• to still support both document paths, do a redirect from one to the other when the document does not exist, but we need to find a smart way to avoid endless redirects
• support only one of the options and redirect the other