Add DIY ESP32S3 N16R8 E22 Back2back board support

This closes #1.

variants/diy_esp32s3_n16r8_e22_back2back/DIYESP32S3N16R8E22Back2backBoard.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include <Arduino.h>
+#include <helpers/ESP32Board.h>
+#include <driver/rtc_io.h>
+
+class DIYESP32S3N16R8E22Back2backBoard : public ESP32Board {
+public:
+  void begin() {
+    ESP32Board::begin();
+
+    esp_reset_reason_t reason = esp_reset_reason();
+    if (reason == ESP_RST_DEEPSLEEP) {
+      long wakeup_source = esp_sleep_get_ext1_wakeup_status();
+      if (wakeup_source & (1 << P_LORA_DIO_1)) {  // received a LoRa packet (while in deep sleep)
+        startup_reason = BD_STARTUP_RX_PACKET;
+      }
+
+      rtc_gpio_hold_dis((gpio_num_t)P_LORA_NSS);
+      rtc_gpio_deinit((gpio_num_t)P_LORA_DIO_1);
+    }
+  }
+
+  void enterDeepSleep(uint32_t secs, int pin_wake_btn = -1) {
+    esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_ON);
+
+    // Make sure the DIO1 and NSS GPIOs are hold on required levels during deep sleep
+    rtc_gpio_set_direction((gpio_num_t)P_LORA_DIO_1, RTC_GPIO_MODE_INPUT_ONLY);
+    rtc_gpio_pulldown_en((gpio_num_t)P_LORA_DIO_1);
+
+    rtc_gpio_hold_en((gpio_num_t)P_LORA_NSS);
+
+    if (pin_wake_btn < 0) {
+      esp_sleep_enable_ext1_wakeup( (1L << P_LORA_DIO_1), ESP_EXT1_WAKEUP_ANY_HIGH);  // wake up on: recv LoRa packet
+    } else {
+      esp_sleep_enable_ext1_wakeup( (1L << P_LORA_DIO_1) | (1L << pin_wake_btn), ESP_EXT1_WAKEUP_ANY_HIGH);  // wake up on: recv LoRa packet OR wake btn
+    }
+
+    if (secs > 0) {
+      esp_sleep_enable_timer_wakeup(secs * 1000000);
+    }
+
+    // Finally set ESP32 into sleep
+    esp_deep_sleep_start();   // CPU halts here and never returns!
+  }
+
+  uint16_t getBattMilliVolts() override {
+    return 0;
+  }
+
+  const char* getManufacturerName() const override {
+    return "DIY ESP32S3 N16R8 E22 Back2back";
+  }
+};