Add M115 Cap:BABYSTEPPING (#17691)

Marlin/src/gcode/host/M115.cpp

     // MOTION_MODES (M80-M89)
     cap_line(PSTR("MOTION_MODES"), ENABLED(GCODE_MOTION_MODES));
 
+    // BABYSTEPPING (M290)
+    cap_line(PSTR("BABYSTEPPING"), ENABLED(BABYSTEPPING));
+
     // CHAMBER_TEMPERATURE (M141, M191)
     cap_line(PSTR("CHAMBER_TEMPERATURE"), ENABLED(HAS_HEATED_CHAMBER));