Add support for TDS and water flow sensors (like SEN0244)

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

DFRobot have a pretty nifty TDS sensor that can be used together with flow meter like linked below.
It would be awesome if ESPHome would give support for such devices.

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

These sensors can be great to detect when a Reverse Osmosis membrane is used up and safe guards agains too much water waste. It can also alert you to when you should exchange generic filters (based on rising TDS numbers).
It can be done now via Arduino and other platforms like MQTT or MySensors, but I'd love to have it all nice and tidy via ESPHome.

**Additional context**

DFRobot product info [here](https://wiki.dfrobot.com/Gravity__Analog_TDS_Sensor___Meter_For_Arduino_SKU__SEN0244)
Sample flow meter/TDS sensor [here](https://www.aliexpress.com/item/32870871997.html)

No repository files, tests, or entry points are identified in the request. Start by reviewing the linked DFRobot SEN0244 product information and flow-meter details, then establish the required sensor behavior and integration scope; done means both TDS and water-flow sensors are supported in ESPHome.

Written by the indexing model from the issue text.