upstream proxy setting

[karlcheong]

I need to use an upstream proxy in order to connect to the kancolle server,
but cant found how to config KCCP to use proxy.

If this functionality is not there please consider to add this functionality.
Using VPN may somehow bypass the problem but it require extra cost and effort, and may not work well every time.

App version: 2.6.3
OS: macOS 11.5.2
Browser: poi 10.7