yml-config: Add support of rootUser and rootPassword (#18615)

Users can define the root user and password in the yaml configuration
file; Root credentials defined in the environment variable still take
precedence

cmd/globals.go

@@ -146,6 +146,8 @@ type serverCtxt struct {
 	configDirSet, certsDirSet bool
 	Interface                 string
 
+	RootUser, RootPwd string
+
 	FTP  []string
 	SFTP []string