Middleware to add the "/" if needed

[trajano]

Just reversed it here but I haven't tested it

@pascalandy

- traefik.http.middlewares.strip-prefix-1.redirectregex.regex=^(https?://[^/]+/[a-z0-9_]+)/$
- traefik.http.middlewares.strip-prefix-1.redirectregex.replacement=${1}

basically the position of the / is swapped.