Signal strength (proxy) for xiaomi_lywsd03mmc

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

I have 4 xiaomi_lywsd03mmc temp / humidity sensors scattered around my house. I currently optimize their locations by moving my Node MCU (the BLE master) or the sensors (BLE slaves) to slightly different positions, then wait for ~12 hours of data to come through. I can tell a good placement by nice consistent readings. A bad placement drops a couple; even truly awful placements will get a few readings in over a 12 hour period.

It would be great if the ESP could track and report (as a first class metric, or in some diagnostic fashion) the average number of reads per hour per device, so I could see if some are doing better than others a little easier. This would also work quite well as a chart to notice when one of them goes offline, since the battery reporting doesn't work (I believe this is a hardware issue, nothing to do with ESPHome).

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

This would be helpful for both device placement / optimization, and dead device detection.

**Additional context**

You can do this manually but it's a lot of work looking at charts.