[Node] Adding a custom log

[Jeel-mehta]

Issue description:
We need a reliable way to validate SigV4 logs across different language implementations (Python, JavaScript, .NET, Java) for our sample applications. The current logging doesn't provide a consistent, easily identifiable log entry for this purpose. This PR adds a standardized SigV4 logging mechanism to the Javascript sample application, similar to what was implemented for Python in PR [#406] and Java in PR [#411]

Description of changes:
Added a custom WARNING log in the aws_sdk_call function of the Python sample application. This custom log will be present in the log-group and can be used to filter logs from those created while running the sample application. This change provides a consistent log entry that can be replicated across other language implementations for uniform SigV4 log validation.

Rollback procedure:

1. Remove the line logger.warn("This is a custom log for validation testing"); from the aws_sdk_call function in index.js of frontend service.
2. Commit and push the change.
3. Redeploy the application.

Testing:
For testing, used a sample app and instrument it with adot js to visualize if the new custom log appears in cloudwatch console. Here is the screenshot of the log from cloudwatch console.

<Can we safely revert this commit if needed? If not, detail what must be done to safely revert and why it is needed.>

Ensure you've run the following tests on your changes and include the link below:

To do so, create a test.yml file with name: Test and workflow description to test your changes, then remove the file for your PR. Link your test run in your PR description. This process is a short term solution while we work on creating a staging environment for testing.

NOTE: TESTS RUNNING ON A SINGLE EKS CLUSTER CANNOT BE RUN IN PARALLEL. See the needs keyword to run tests in succession.

• Run Java EKS on e2e-playground in us-east-1 and eu-central-2
• Run Python EKS on e2e-playground in us-east-1 and eu-central-2
• Run metric limiter on EKS cluster e2e-playground in us-east-1 and eu-central-2
• Run EC2 tests in all regions
• Run K8s on a separate K8s cluster (check IAD test account for master node endpoints; these will change as we create and destroy clusters for OS patching)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.