I don’t think AOSP has global http proxy support implemented - Samsung Knox has though - Knox PAC Support (Proxy Auto Config)
There is a thread with a user supplying Squid as http proxy via pac for Wifi. While that thread was about app-lounge (not) respecting the proxy settings, after reading around it seemed it is increasingly hard to use http proxies to filter/inspect device traffic as not all Apps will respect the supplied proxy address.