In PR https://github.com/10gen/mongo/pull/46535, tests were added in api_boundary_server_status.js which check the success/failure observability metrics for extensions. 

To improve readability and maintenance, we should leverage the existing extension metrics helpers in extension_stage_command_metrics.js (i.e observeExtensionMetricsChange) in this test.

As part of this ticket, adjust this helper and use it in api_boundary_server_status.js.