support user certificate

[patterniha]

please support user-certificate that has been added to android system

usage:

• subscriptions with a self-signed certificate
• Xray-core built-in DOH can connect to a private DOH-server with a self-signed certificate.

you should add support-line to the app's manifest https://github.com/2dust/v2rayNG/blob/4a653d49358caf642669c84f6d3a8bd4f93491c6/V2rayNG/app/src/main/AndroidManifest.xml

help:

• link1, link2, link3