nginxplus_location_zone_* metrics are missing in the exported metrics

[haselere]

Describe the bug
nginxplus_location_zone_* metrics are missing in the exported metrics calling http://localhost:9113/metrics

To reproduce
Steps to reproduce the behavior:

1. Start nginx plus instance and Expose the built-in metrics in NGINX Plus:
   For NGINX Plus, expose the API at /api on port 8080.
2. curl metrics endpoint and see all metrics (http://localhost:9113/metrics) - no nginxplus_location_zone_* are available

Expected behavior
nginxplus_location_zone_* should be available

Your environment

• Version of the Prometheus exporter - https://github.com/nginx/nginx-prometheus-exporter/releases/tag/v1.5.1
• Using NGINX Plus

[nginx-bot]

Hi @haselere! Welcome to the project! 🎉

Thanks for opening this issue!
Be sure to check out our Contributing Guidelines and the Issue Lifecycle while you wait for someone on the team to take a look at this.