redirect `xxxx/current` to `xxx/current/`

`https://pekko.apache.org/docs/pekko/current` will be a 404 website
it should be redirected to `https://pekko.apache.org/docs/pekko/current/`

Start by locating the site's redirect or routing configuration for /docs/pekko/current and verify how the trailing-slash URL is handled. Reproduce the current 404, then confirm that /docs/pekko/current redirects to /docs/pekko/current/ and that the destination loads successfully.

Written by the indexing model from the issue text.