Bring in safe mode support (#8478)

This PR refactors object layer handling such
that upon failure in sub-system initialization
server reaches a stage of safe-mode operation
wherein only certain API operations are enabled
and available.

This allows for fixing many scenarios such as

 - incorrect configuration in vault, etcd,
   notification targets
 - missing files, incomplete config migrations
   unable to read encrypted content etc
 - any other issues related to notification,
   policies, lifecycle etc

pkg/color/color.go

@@ -37,6 +37,13 @@ var (
 		return fmt.Sprint
 	}()
 
+	RedBold = func() func(format string, a ...interface{}) string {
+		if IsTerminal() {
+			return color.New(color.FgRed, color.Bold).SprintfFunc()
+		}
+		return fmt.Sprintf
+	}()
+
 	Red = func() func(format string, a ...interface{}) string {
 		if IsTerminal() {
 			return color.New(color.FgRed).SprintfFunc()