Handle incorrect scheme when accessing via ngrok

[lornajane]

When switching between using this example directly on http://localhost:8080 and the same but with ngrok in front https://somethingsomething.ngrok.io then we lose the scheme* and it always assumes HTTP, not HTTPS, because it ignores the HTTP_X_FORWARDED_PROTO for security reasons. For this situation, where we want to support the header, we can use https://github.com/akrabat/rka-scheme-and-host-detection-middleware.

This pull request adds it for the record-a-message building block only, but if we agree this is useful, I'll roll it out for the others (4 or 5 others in the voice folder using Slim are affected I think , it's basically when we need to build a URL in an NCCO).

• Actually we also get the wrong port number, but I think that's a Slim bug and have opened an issue/PR with them and am leaving our code as it is for now (see https://github.com/slimphp/Slim/issues/2486)

[lornajane]

probably outdated

[dragonmantank]

Yeah, I don't think it's been an issue since the later 3.x builds and doesn't seem to be an issue in 4.x