Expose INA219 measurement as battery voltage for Seeed Xiao ESP32S3

[syssi]

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The Meshtastic firmware lacks the ability to publish INA power monitor measurements as battery voltage readings when BATTERY_PIN is not defined. This limitation affects users who want to monitor battery levels using INA sensors.

Additionally, when a valid GPIO/A0 pin is assigned as BATTERY_PIN, users can measure analog voltage directly through that pin without requiring firmware recompilation. This feature provides more flexibility for hardware configurations.

This improvement would benefit users by:

1. Enabling battery voltage monitoring through INA sensors even without a dedicated battery pin
2. Allowing dynamic analog voltage measurements through GPIO pins
3. Reducing the need for custom firmware builds

Related issues:

https://github.com/meshtastic/firmware/issues/5248 https://github.com/meshtastic/firmware/issues/5880