New input plugin: `input.upower`

### Use Case

Monitoring laptop batteries and batteries of connected peripherals. Upower is the standard way of reporting battery information in Linux. UPS devices might also report their level using upower but I'm not sure if it's common, I don't have any UPSs to test with.

### Expected behavior

Batteries can be monitored using a upower input plugin.

### Actual behavior

None, batteries need to be monitored using manual workarounds like the `exec` input plugin.

### Additional info

_No response_

The issue names no files or tests. Start by reviewing existing Telegraf input plugins and the UPower interface; done means a plugin can expose laptop and peripheral battery metrics, with behavior verified on supported Linux systems.

Written by the indexing model from the issue text.