💡 Rename build_info metric to cloudflared_build_info

**Describe the feature you'd like**
The current name of build_info is very generic, which means it can be hard to find or can be easily mixed with other metrics.

**Describe alternatives you've considered**
Add to add a new label to the metric processing to make it easier to identify.

**Additional context**
It is a common pattern for other Prometheus metrics exporters. Given it could be a breaking change, might make sense to duplicate it to `cloudflared_build_info` first.