create SPIFFS logger function

FDRS_Gateway/FDRS_Gateway.ino

@@ -69,6 +69,9 @@ void setup() {
 #ifdef USE_SD_LOG
   begin_SD();
 #endif
+#ifdef USE_SPIFFS_LOG
+  begin_FS();
+#endif
   
   //DBG(sizeof(DataReading));
 #ifdef USE_WIFI

FDRS_Gateway/fdrs_config.h

@@ -19,6 +19,7 @@
 //#define USE_LORA
 //#define USE_WIFI      //Used only for MQTT gateway
 //#define USE_SD_LOG      //Used only for SD-card logging
+//#define USE_SPIFFS_LOG      //Used only for SPIFFS logging (esp internal filesystem)
 
 // Peer addresses
 #define ESPNOW1_PEER  0x0E  // ESPNOW1 Address 
@@ -83,4 +84,7 @@
 
 // SD card logging config -- Needed only for SD-card logging
 #define SD_SS 0     //SD card Chipselect pin (Use a different pins for LoRa and SD)
-#define SD_FILENAME "fdrs_log.csv"  // length max. 32
+#define SD_FILENAME "fdrs_log.csv"  // length max. 32
+
+// SPIFFS logging config -- Needed only for SPIFFS logging
+#define SPIFFS_FILENAME "fdrs_log.csv"  // length max. 32