fix Type confusion through parameter tampering

[odaysec]

https://github.com/aws-amplify/amplify-cli/blob/aaef95c5a46232fac5105201c490210ac67c93b7/packages/amplify-storage-simulator/src/server/utils.ts#L77-L77

fix the issue need to ensure that the buf parameter in the stripChunkSignature function is of the expected type (Buffer). If buf is not a Buffer, the function should either throw an error or return the input unchanged, depending on the desired behavior. This can be achieved by adding a runtime type check at the beginning of the function.

1. Add a type check to verify that buf is a Buffer using Buffer.isBuffer(buf).
2. If the check fails, return the input unchanged or handle the error appropriately.
3. This change ensures that the function behaves predictably even if buf is tampered with.

---

Checklist

• [x] PR description included
• [x] yarn test passes
• [x] Tests are changed or added
• [x] Relevant documentation is changed or added (and PR referenced)
• [x] New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• [x] Pull request labels are added

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