Fix review comments and new changes in config (#8515)

- Migrate and save only settings which are enabled
- Rename logger_http to logger_webhook and
  logger_http_audit to audit_webhook
- No more pretty printing comments, comment
  is a key=value pair now.
- Avoid quotes on values which do not have space in them
- `state="on"` is implicit for all SetConfigKV unless
  specified explicitly as `state="off"`
- Disabled IAM users should be disabled always

cmd/server-startup-msg.go

@@ -199,6 +199,10 @@ func printServerCommonMsg(apiEndpoints []string) {
 
 // Prints bucket notification configurations.
 func printEventNotifiers() {
+	if globalNotificationSys == nil {
+		return
+	}
+
 	arns := globalNotificationSys.GetARNList()
 	if len(arns) == 0 {
 		return