feat: [cloudwatch][LogMonitoring] added logStream field to query (#86)

Added logStream to the query so the end user can easily do further investigation

`npm test` passes

Fixes #85

---

_By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license_

Author: rahul0705

lib/monitoring/aws-cloudwatch/LogMonitoring.ts

@@ -71,7 +71,7 @@ export class LogMonitoring extends Monitoring {
          * https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/CWL_QuerySyntax.html
          */
         queryLines: [
-          "fields @timestamp, @message",
+          "fields @timestamp, @logStream, @message",
           `filter @message like /${this.pattern}/`,
           "sort @timestamp desc",
           `limit ${this.limit}`,