fix: resolve 'Received spot notification for undefined' log message

When metrics are disabled, metricName is undefined and gets interpolated
into the log string as literal "undefined". Use conditional interpolation
so the message reads "Received spot notification" when no metric is set.

Author: jensenbox

lambdas/functions/termination-watcher/src/metric-event.ts

@@ -13,7 +13,7 @@ export async function metricEvent(
   const instanceRunningTimeInSeconds = instance.LaunchTime
     ? (new Date(event.time).getTime() - new Date(instance.LaunchTime).getTime()) / 1000
     : undefined;
-  logger.info(`Received spot notification for ${metricName}`, {
+  logger.info(`Received spot notification${metricName ? ` for ${metricName}` : ''}`, {
     instanceId: instance.InstanceId,
     instanceType: instance.InstanceType ?? 'unknown',
     instanceName: instance.Tags?.find((tag) => tag.Key === 'Name')?.Value,