Add Singapore Region

Add 433MHz, 868MHz and 923MHz bands for Singapore.

Regulatory reference: https://www.imda.gov.sg/-/media/imda/files/regulation-licensing-and-consultations/ict-standards/telecommunication-standards/radio-comms/imdatssrd.pdf bands 26a , 29 and 30c.

src/mesh/RadioInterface.cpp

@@ -123,6 +123,17 @@ const RegionInfo regions[] = {
     */
     RDEF(MY_919, 919.0f, 924.0f, 100, 0, 27, true, true, false),
 
+    /*
+        Singapore
+        SG_433 Band 26a: 433.05 - 434.79 MHz at 10mW, 10% duty cycle.
+        SG_868 Band 29: 868 - 869 MHz at 500mW, no restrictions.
+        SG_923 Band 30c: 917 - 925 MHz at 100mW, 1% duty cycle.
+        https://www.imda.gov.sg/-/media/imda/files/regulation-licensing-and-consultations/ict-standards/telecommunication-standards/radio-comms/imdatssrd.pdf
+    */
+    RDEF(SG_433, 433.05f, 434.79f, 10, 0, 10, true, false, false),
+    RDEF(SG_868, 868.0f, 869.0f, 100, 0, 27, true, false, false),
+    RDEF(SG_923, 917.0f, 925.0f, 1, 0, 20, true, false, false),
+
     /*
        2.4 GHZ WLAN Band equivalent. Only for SX128x chips.
     */

src/mesh/generated/meshtastic/config.pb.h

@@ -214,7 +214,13 @@ typedef enum _meshtastic_Config_LoRaConfig_RegionCode {
     /* Malaysia 433mhz */
     meshtastic_Config_LoRaConfig_RegionCode_MY_433 = 16,
     /* Malaysia 919mhz */
-    meshtastic_Config_LoRaConfig_RegionCode_MY_919 = 17
+    meshtastic_Config_LoRaConfig_RegionCode_MY_919 = 17,
+    /* Singapore 433mhz */
+    meshtastic_Config_LoRaConfig_RegionCode_SG_433 = 18,
+    /* Singapore 868mhz */
+    meshtastic_Config_LoRaConfig_RegionCode_SG_868 = 19,
+    /* Singapore 923mhz */
+    meshtastic_Config_LoRaConfig_RegionCode_SG_923 = 20
 } meshtastic_Config_LoRaConfig_RegionCode;
 
 /* Standard predefined channel settings