Add support for Z2 min endstop to M119

Marlin/endstops.cpp

     SERIAL_PROTOCOLPGM(MSG_Z_MIN);
     SERIAL_PROTOCOLLN(((READ(Z_MIN_PIN)^Z_MIN_ENDSTOP_INVERTING) ? MSG_ENDSTOP_HIT : MSG_ENDSTOP_OPEN));
   #endif
+  #if HAS_Z2_MIN
+    SERIAL_PROTOCOLPGM(MSG_Z2_MIN);
+    SERIAL_PROTOCOLLN(((READ(Z2_MIN_PIN)^Z2_MIN_ENDSTOP_INVERTING) ? MSG_ENDSTOP_HIT : MSG_ENDSTOP_OPEN));
+  #endif
   #if HAS_Z_MAX
     SERIAL_PROTOCOLPGM(MSG_Z_MAX);
     SERIAL_PROTOCOLLN(((READ(Z_MAX_PIN)^Z_MAX_ENDSTOP_INVERTING) ? MSG_ENDSTOP_HIT : MSG_ENDSTOP_OPEN));

Marlin/language.h

 #define MSG_Y_MAX                           "y_max: "
 #define MSG_Z_MIN                           "z_min: "
 #define MSG_Z_MAX                           "z_max: "
+#define MSG_Z2_MIN                          "z2_min: "
 #define MSG_Z2_MAX                          "z2_max: "
 #define MSG_Z_PROBE                         "z_probe: "
 #define MSG_ERR_MATERIAL_INDEX              "M145 S<index> out of range (0-1)"