TLS client: Use Xray-core's built-in RootCAs by default (avoids maliciously injected CA in the OS) (#7105)

https://github.com/XTLS/Xray-core/pull/5532#issuecomment-3745598515
https://github.com/XTLS/Xray-core/pull/7098#issuecomment-6053012480
https://github.com/XTLS/Xray-core/pull/7105#issuecomment-6093006914

infra/conf/transport_security.go

@@ -316,6 +316,7 @@ type TLSConfig struct {
 	ECHServerKeys           string           `json:"echServerKeys"`
 	ECHConfigList           string           `json:"echConfigList"`
 	ECHSocketSettings       *SocketConfig    `json:"echSockopt"`
+	UseSystemCA             bool             `json:"useSystemCA"`
 }
 
 // Build implements Buildable.
@@ -403,6 +404,7 @@ func (c *TLSConfig) Build() (proto.Message, error) {
 		}
 		config.EchSocketSettings = ss
 	}
+	config.UseSystemCa = c.UseSystemCA
 
 	return config, nil
 }