exporters/prometheus/internal/x: generate `x` package from `x` component template

Idea from https://github.com/open-telemetry/opentelemetry-go/pull/7361

- Ref: https://github.com/open-telemetry/opentelemetry-go/pull/7361
- Components that need to be processed: [exporters/prometheus/internal/x](https://github.com/open-telemetry/opentelemetry-go/blob/60f9f39d78d87239098dbe8f07ebc1f2f37be8f4/exporters/prometheus/internal/x)