Added new Forwarded header support for Request::getClientIps

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11073
| License       | MIT
| Doc PR        | no
@Seldaek I can't add a test for ips like `[2001:db8:cafe::17]:4711` as it is later rejected by the `IpUtils::checkIp` call. What do you suggest?