WIP #16543 add directives to add or remove trailing slash

Added two directives as said in #16543.

Need to discuss:
- The location of the directives: `PathDirectives` or `RouteDirectives`?
- Returning status code to redirect: 301, 302 or make it configurable? 
- More tests
- More documentation
- etc.
Currently yes. In which cases would you want to distinguish between

```
GET /foo HTTP/1.1
Host: example.com:80
```

and


```
GET http://example.com/bar/../foo HTTP/1.1
Host: example.com
```

?