[BT] Add BM2 voltage (#1495)

* [BT] Add BM2 voltage

Voltage retrieval through a BLE connection, frequency of the BLE connection is defined by `intervalcnct`

* Add doc

Credits to https://github.com/KrystianD/bm2-battery-monitor

main/ZgatewayBLEConnect.ino

@@ -4,7 +4,6 @@
 #    include "ArduinoJson.h"
 #    include "ArduinoLog.h"
 #    include "ZgatewayBLEConnect.h"
-
 #    define convertTemp_CtoF(c) ((c * 1.8) + 32)
 
 extern bool ProcessLock;
@@ -255,6 +254,81 @@ void DT24_connect::publishData() {
   }
 }
 
+/*-----------------------BM2 HANDLING-----------------------*/
+void BM2_connect::notifyCB(NimBLERemoteCharacteristic* pChar, uint8_t* pData, size_t length, bool isNotify) {
+  if (m_taskHandle == nullptr) {
+    return; // unexpected notification
+  }
+
+  if (!ProcessLock) {
+    Log.trace(F("Callback from %s characteristic" CR), pChar->getUUID().toString().c_str());
+    if (length == 16) {
+      Log.trace(F("Device identified creating BLE buffer" CR));
+      JsonObject& BLEdata = getBTJsonObject();
+      String mac_address = m_pClient->getPeerAddress().toString().c_str();
+      mac_address.toUpperCase();
+      BLEdata["model"] = "BM2 Battery Monitor";
+      BLEdata["id"] = (char*)mac_address.c_str();
+      mbedtls_aes_context aes;
+      mbedtls_aes_init(&aes);
+      unsigned char output[16];
+      unsigned char iv[16] = {};
+      unsigned char key[16] = {
+          108,
+          101,
+          97,
+          103,
+          101,
+          110,
+          100,
+          255,
+          254,
+          49,
+          56,
+          56,
+          50,
+          52,
+          54,
+          54,
+      };
+      mbedtls_aes_setkey_dec(&aes, key, 128);
+      mbedtls_aes_crypt_cbc(&aes, MBEDTLS_AES_DECRYPT, 16, iv, (uint8_t*)&pData[0], output);
+      mbedtls_aes_free(&aes);
+      float volt = ((output[2] | (output[1] << 8)) >> 4) / 100.0f;
+      BLEdata["volt"] = volt;
+      Log.trace(F("volt: %F" CR), volt);
+      pubBT(BLEdata);
+    } else {
+      Log.notice(F("Invalid notification data" CR));
+      return;
+    }
+  } else {
+    Log.trace(F("Callback process canceled by processLock" CR));
+  }
+
+  xTaskNotifyGive(m_taskHandle);
+}
+
+void BM2_connect::publishData() {
+  NimBLEUUID serviceUUID("fff0");
+  NimBLEUUID charUUID("fff4");
+  NimBLERemoteCharacteristic* pChar = getCharacteristic(serviceUUID, charUUID);
+
+  if (pChar && pChar->canNotify()) {
+    Log.trace(F("Registering notification" CR));
+    if (pChar->subscribe(true, std::bind(&BM2_connect::notifyCB, this,
+                                         std::placeholders::_1, std::placeholders::_2,
+                                         std::placeholders::_3, std::placeholders::_4))) {
+      m_taskHandle = xTaskGetCurrentTaskHandle();
+      if (ulTaskNotifyTake(pdTRUE, pdMS_TO_TICKS(BLE_CNCT_TIMEOUT)) == pdFALSE) {
+        m_taskHandle = nullptr;
+      }
+    } else {
+      Log.notice(F("Failed registering notification" CR));
+    }
+  }
+}
+
 /*-----------------------HHCCJCY01HHCC HANDLING-----------------------*/
 void HHCCJCY01HHCC_connect::publishData() {
   NimBLEUUID serviceUUID("00001204-0000-1000-8000-00805f9b34fb");