Add observability rule for metrics name changes

[Essekar]

Summary

Add observability rule to detect metric name changes that could break
production dashboards and alerts.

Rule Details

• ID: observability.metrics.metric-name-change
• Severity: WARNING
• Languages: JavaScript, TypeScript, Python, Go
• Purpose: Flags when developers change metric names, requiring
  dashboard/alert updates

Test Cases

• 6 true positives (detects various metric patterns)
• 9 true negatives (ignores non-metric code)

Use Case

Prevents production monitoring breakage when developers refactor metric
names without updating:

• Grafana dashboards
• Alert rules
• SLA monitoring

Example Detection

// This would be flagged for review:
metrics.counter("user_login_count", 1);
prometheus.Counter({name: "http_requests_total", help: "..."});
statsd.increment("page_views", 1);

Impact

Helps teams catch observability breaking changes in CI before they reach
production, preventing monitoring blind spots.

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