feat: purge old provisioner daemons (#10949)

coderd/database/queries/provisionerdaemons.sql

@@ -11,7 +11,18 @@ INSERT INTO
 		created_at,
 		"name",
 		provisioners,
-		tags
+		tags,
+		updated_at
 	)
 VALUES
-	($1, $2, $3, $4, $5) RETURNING *;
+	($1, $2, $3, $4, $5, $6) RETURNING *;
+
+-- name: DeleteOldProvisionerDaemons :exec
+-- Delete provisioner daemons that have been created at least a week ago
+-- and have not connected to coderd since a week.
+-- A provisioner daemon with "zeroed" updated_at column indicates possible
+-- connectivity issues (no provisioner daemon activity since registration).
+DELETE FROM provisioner_daemons WHERE (
+	(created_at < (NOW() - INTERVAL '7 days') AND updated_at IS NULL) OR
+	(updated_at IS NOT NULL AND updated_at < (NOW() - INTERVAL '7 days'))
+);