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

internal/config/server.go

@@ -32,6 +32,8 @@ type Opts struct {
 // ServerConfig represents a MinIO configuration file
 type ServerConfig struct {
 	Version     string     `yaml:"version"`
+	RootUser    string     `yaml:"rootUser"`
+	RootPwd     string     `yaml:"rootPassword"`
 	Addr        string     `yaml:"address"`
 	ConsoleAddr string     `yaml:"console-address"`
 	CertsDir    string     `yaml:"certs-dir"`