Fix getting metrics list from env (#4891)

# What this PR does

## Which issue(s) this PR closes

Related to [issue link here]

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## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated
- [x] Documentation added (or `pr:no public docs` PR label added if not
required)
- [x] Added the relevant release notes label (see labels prefixed w/
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engine/settings/base.py

@@ -117,7 +117,7 @@ METRICS_ALL = [
     METRIC_USER_WAS_NOTIFIED_OF_ALERT_GROUPS_NAME,
 ]
 # List of metrics to collect. Collect all available application metrics by default
-METRICS_TO_COLLECT = os.environ.get("METRICS_TO_COLLECT", METRICS_ALL)
+METRICS_TO_COLLECT = getenv_list("METRICS_TO_COLLECT", METRICS_ALL)
 
 
 # Database