Alerting: Support reusable query templates with placeholders in the UI

### **What problem are you trying to solve?** In Grafana Alerting, alert rules require each team or service to define its own query logic, even when the underlying condition is conceptually the same. This leads to: • duplicated alert queries across teams, • inconsistencies in how similar alerts are implemented, • high maintenance cost when a common query needs to be updated, • reliance on copying/pasting queries instead of reusing shared definitions. Grafana currently lacks a first-class mechanism to reuse alert query logic across alert rules. ⸻ ### **Important clarification**: this is NOT about dashboard template variables Several existing issues and discussions focus on supporting dashboard template variables in alert queries. The following issues and discussions are often referenced in relation to templating in alerting, but they do not fully address the use case described here: • #6557 – “Alerting support for queries using template variables” • #9334 – “Alerting with template variables” • #16681 – “Alerting does not support template variables” • #36110 – “Template variables are not supported in alert queries” • Discussion #39249 – “Allow Template Variables To Be Used in Alert Queries” • #76596 – “Add variable interpolation when creating alert rule from panel” 👉 None of the above propose a UI-level concept of reusable alert query templates with placeholders, defined once and instantiated multiple times with different values. This proposal addresses a different and more general problem. ⸻ ### **Proposed solution** Introduce Query Templates as a first-class concept in Grafana Alerting. A query template would: • Define a query once (PromQL, LogQL, etc.) • Contain explicit placeholders (e.g. ${service}, ${namespace}, ${cluster}) • Be stored and managed centrally • Be selectable from the Alert Rule UI When a user selects a query template: • The UI detects placeholders • The UI prompts for values • The alert rule is instantiated from the template + pr…