Add support for Soil Moisture Sensor (SoMoSe) from BeFle

**Describe the problem you have/What new integration you would like**

I bought a Soil Moisture Sensor from BeFlE which is called SoMoSe (v2.2).
https://github.com/BeFlE/SoMoSe
I got it working using the analog Pin of the Sensor and have readings in Esphome/HomeAssistant.
But i was not able to integrate the digital I²C Sensor in Esphome as i am not so skilled with programming.
I read the Documentation about Custom Sensors but again ... i am not a programmer and did not succeed.

**Please describe your use case for this integration and alternatives you've tried:**

Get Soil Moisture Readings for my Chiliplants via the digital Sensor (I²C) from BeFlE SoMoSe Sensor.
Analog is working but not very accurate.

**Additional context**

Start with the linked BeFle SoMoSe repository and ESPHome's Custom Sensors documentation, then determine how the sensor's digital I²C interface exposes readings. Done means ESPHome can integrate the SoMoSe v2.2 digital sensor and provide soil-moisture readings for Home Assistant; the issue names no project files or tests.

Written by the indexing model from the issue text.