Support X-Forwarded-Host in proxy-headers

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Is your feature related to a problem? Please describe.

When using uvicorn, with starlette URLs with url_for are generated with bad host, when application is behind proxy and proxy sets original host to X-Forwarded-Host.

https://github.com/encode/starlette/issues/604

Describe the solution you would like.

Currently uvicorn uses only X-Forwarded-Proto, X-Forwarded-For, X-Forwarded-Port to populate scope with remote information. But there is X-Forwarded-Host header, which should be used for populating server information in scope.