Use of IAM roles instead of access key for uploads to s3

[agrlayush]

The application currently uses IAM access key to upload objects to s3 buckets. Storing access key directly in the server is not recommended as might lead to security breach and leakage of the access keys.

Best practices suggest to attach IAM role to the AWS Instance, generate temporary credentials to access S3 and other AWS resources.

[agrlayush]

Fixed and created a pull request: #26