[format utils] add missing include for readability

Author: sharder996

src/client/cli/formatter/format_utils.cpp

@@ -22,6 +22,7 @@
 #include <multipass/cli/table_formatter.h>
 #include <multipass/cli/yaml_formatter.h>
 
+#include <locale>
 #include <sstream>
 
 namespace mp = multipass;