Add ADS1X15 voltage metrics (#711)

* Add ADS1X15 voltage metrics
* Add 8 channels to allow for daisy chaining of ADS1X15

meshtastic/telemetry.proto

@@ -188,6 +188,56 @@ message PowerMetrics {
    * Current (Ch3)
    */
   optional float ch3_current = 6;
+
+  /*
+   * Voltage (Ch4)
+   */
+  optional float ch4_voltage = 7;
+
+  /*
+   * Current (Ch4)
+   */
+  optional float ch4_current = 8;
+
+  /*
+   * Voltage (Ch5)
+   */
+  optional float ch5_voltage = 9;
+
+  /*
+   * Current (Ch5)
+   */
+  optional float ch5_current = 10;
+
+  /*
+   * Voltage (Ch6)
+   */
+  optional float ch6_voltage = 11;
+
+  /*
+   * Current (Ch6)
+   */
+  optional float ch6_current = 12;
+
+  /*
+   * Voltage (Ch7)
+   */
+  optional float ch7_voltage = 13;
+
+  /*
+   * Current (Ch7)
+   */
+  optional float ch7_current = 14;
+
+  /*
+   * Voltage (Ch8)
+   */
+  optional float ch8_voltage = 15;
+
+  /*
+   * Current (Ch8)
+   */
+  optional float ch8_current = 16;
 }
 
 /*
@@ -652,6 +702,11 @@ enum TelemetrySensorType {
    * PCT2075 Temperature Sensor
    */
   PCT2075 = 39;
+
+  /*
+   * ADS1X15 ADC
+   */
+  ADS1X15 = 40;
 }
 
 /*