Add Subscription support

[linehman]

Welcome

• Yes, I'm using the latest major release. Only such installations are supported.
• Yes, I'm using the supported system. Only such systems are supported.
• Yes, I've searched similar issues on GitHub and didn't find any.
• Yes, I've included all information below (version, config, log, etc).

Description of the problem,screencshot would be good

Hi, It would have been great if there was support for subscription links , so users could easily get the latest configs availabe on the server. Currently all major v2ray clients support subscription links.

kind regards

Version of x-ui

$ x-ui version
# Paste output here

x-ui log or xray log

# paste log here

[DeAref]

nice idea