Update alerts postgresql metadata.yaml (#1240)

The id should match the file name of the Alert Policy Template.

Our intern found this issue while developing their internship project. Since they don't have access to GitHub, I'm making this change on their behalf

Author: SamiSousa

alerts/postgresql/metadata.yaml

@@ -1,5 +1,5 @@
 alert_policy_templates:
-  - id: "high-connections-utilization"
+  - id: "high-connection-utilization"
     display_name: "Postgresql - High Connection Utilization"
     description: "Alert fires when active connections are near a threshold of 90. Around this point is where the instance may run into connection issues and may start refusing connections."
     version: 1