Feat: Explicitly set fastcgi_params

[steveworley]

When looking to correctly surface true client IP with a number of reverse proxies in the mix we need access to the X_FORWARDED_FOR header in Drupal. With the default configuration this presents as a single IP address for the last hop in the chain:

$_SERVER['HTTP_X_FORWARDED_FOR']	127.0.0.1 (last hop)

With this change we explicitly set X_FORWARDED_FOR and other useful request identifiers back via fastcgi_params. This allows us to use reverse_proxy_addresses correctly in Drupal (and other applications analogs) to correctly act on the true client IP.

With this change PHP sees the following:

$_SERVER['HTTP_X_FORWARDED_FOR']	127.0.0.1 (last hop), 1.1.1.1 (remote_addr)

$proxy_add_x_forwarded_for appends the remote_addr to the IP list to allow us to access that information. PHP currently does not see the value set in the proxy_set_header and this was the only way I was able to surface this to PHP.

[seanhamlin]

Make sense to me. Likely will need to be called out in the release notes that X-Forwarded-For will contain the chain of IPs (which is more normal anyway).