Add HISTORY_INTERVAL_MILLISECONDS constant for saving history data

platformio.ini

@@ -91,6 +91,7 @@ build_flags =
     -DRED_PIN_HIGH=1    	; Should the RED_PIN_HIGH go high or low at threshold
     -DPIN_HYSTERESIS=100    ; Hysteresis PPM to avoid pins going ON and OFF continuously. TODO : Minimum time to switch
     -DBUZZER_HYSTERESIS=50  ; Hysteresis PPM to avoid BUZZER ON and OFF
+    -DHISTORY_INTERVAL_MILISECONDS=60000 ; Interval in miliseconds to save history data (60000 = 1 minute)
     -DHISTORY_RING_BUFFER_SIZE_BYTES=10000 ; Number of samples to keep in history for MyAmbiance. Try to save memory by using just what you need (recommended < 10000 for boards without PSRAM).
 
     -DMQTT_DISCOVERY_PREFIX="\"homeassistant/\""