## Description
This PR implements extraction of metrics defined using the `prometheus.NewDesc()` pattern.
## Changes
* Add `extractNewDescMetric()` to extract metrics from `prometheus.NewDesc()` calls
* Script generates an updated `scripts/metricsdocgen/generated_metrics` file
Related to: https://github.com/coder/coder/issues/13223
**Disclosure:** This PR was mainly developed with Claude Sonnet 4, with iterative review and refinement by @ssncferreira