Publish battery level and firmware version for xiaomi_hhccjcy01

**Describe the problem you have/What new integration you would like**
I have a bunch of these sensors on firmware levels 3.2.2 and 3.2.4. They work just fine except for battery level, and I thought it would be nice if the firmware level was published as well.

**Please describe your use case for this integration and alternatives you've tried:**
It would be nice to be able to monitor the battery level to enable low battery notifications.

**Additional context**
I read through https://github.com/esphome/esphome/pull/1288 where it's stated that the battery level is no longer broadcast
since firmware 3.2.1. I just installed the WatchFlower app and that shows both battery level and firmware level, so the data must be accessible.

I'm not an expert on Bluetooth, but I'm guessing getting those two values might require a question/response something instead of just listening passively and that's why battery level no longer is shown?

No source file, test, or entry point is named. Start by reviewing PR #1288 and investigating how the WatchFlower app obtains battery and firmware values from firmware 3.2.2 and 3.2.4. Done means publishing both values for xiaomi_hhccjcy01 and verifying that battery data supports low-battery notifications.

Written by the indexing model from the issue text.