Usermod SensorsToMqtt: Add bmp280+ccs811+si7021 sensors to wled and publish them via MQTT to Home Assistant (#1588)

* Adding SensorsToMqtt usermod, which allows WLED to read bmp280/SI7021/CCS811 sensors and publish it via MQTT to e.g. Home Assistant.

* undo some changes we dont want upstream

* undo some changes we dont want upstream2

Co-authored-by: Machiel Pronk <machiel.pronk89@gmail.com>

usermods/sensors_to_mqtt/readme.md

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+# Sensors To Home Assistant (or mqtt)
+
+This usermod will publish values of the BMP280, CCS811 and Si7021 sensors to Home Assistant via MQTT.
+
+Its using home assistant automatic device discovery feature.
+
+The use of Home Assistant is not mandatory; it will publish the sensor values via MQTT just fine without it.
+
+Its resusing the mqtt connection set in the WLED web user interface.
+
+## Maintainer
+
+twitter.com/mpronk89
+
+## Features
+
+- Reads BMP280, CCS811 and Si7021 senors
+- Publishes via MQTT, configured via webui of wled
+- Announces device in Home Assistant for easy setup
+- Efficient energy usage
+- Updates every 60 seconds
+
+## Example mqtt topics:
+
+`$mqttDeviceTopic` is set in webui of WLED!
+
+```
+temperature: $mqttDeviceTopic/temperature
+pressure: $mqttDeviceTopic/pressure
+humidity: $mqttDeviceTopic/humidity
+tvoc: $mqttDeviceTopic/tvoc
+eCO2:  $mqttDeviceTopic/eco2
+IAQ:  $mqttDeviceTopic/iaq
+```
+
+# Installation
+
+## Hardware
+
+### Requirements
+
+1. BMP280/CCS811/Si7021 sensor. E.g. https://aliexpress.com/item/32979998543.html
+2. A microcontroller which can talk i2c, e.g. esp32
+
+### installation
+
+Attach the sensor to the i2c interface.
+
+Default PINs esp32:
+
+```
+SCL_PIN = 22;
+SDA_PIN = 21;
+```
+
+Default PINs ESP8266:
+
+```
+SCL_PIN = 5;
+SDA_PIN = 4;
+```
+
+## Enable in WLED
+
+1. Copy `usermod_v2_SensorsToMqtt.h` into the `wled00` directory.
+2. Add to `build_flags` in platformio.ini:
+
+```
+  -D USERMOD_SENSORSTOMQTT
+```
+
+3. And add to `lib_deps` in platformio.ini:
+
+```
+  adafruit/Adafruit BMP280 Library @ 2.1.0
+  adafruit/Adafruit CCS811 Library @ 1.0.4
+  adafruit/Adafruit Si7021 Library @ 1.4.0
+```
+
+The #ifdefs in `usermods_list.cpp` should do the rest :)
+
+# Credits
+
+- Aircoookie for making WLED
+- Other usermod creators for example code
+- Bouke_Regnerus for https://community.home-assistant.io/t/example-indoor-air-quality-text-sensor-using-ccs811-sensor/125854
+- You, for reading this