feat(draw/sw): make I1 luminance threshold configurable (#7616)

lv_conf_template.h

@@ -174,6 +174,10 @@
     #define LV_DRAW_SW_SUPPORT_A8           1
     #define LV_DRAW_SW_SUPPORT_I1           1
 
+    /* The threshold of the luminance to consider a pixel as
+     * active in indexed color format */
+    #define LV_DRAW_SW_I1_LUM_THRESHOLD 127
+
     /** Set number of draw units.
      *  - > 1 requires operating system to be enabled in `LV_USE_OS`.
      *  - > 1 means multiple threads will render the screen in parallel. */