serve http/webdav: redirect requests to the base url without the /
serve http/webdav: redirect requests to the base url without the /

When using `--baseurl` before this patch, if a request was made to the
base URL without a trailing / then rclone would return a 404 error.

Unfortunately GVFS / Nautilus makes the request without the /
regardless of what the user put in.

This patch redirects the request to the base URL with a /. So if the
user was using `--baseurl rclone` then a request to
http://localhost/rclone would be redirected with a 308 response to
http://localhost/rclone/

Fixes #4814

ncw/rclone,ncw/rclone,ncw/rclone,ncw/rclone