Add robot tests for S3Gateway API's using curl calls

This Jira is added to add robot tests using curl calls for S3 EndPoints.

As we have observed that there is some difference in (handling input and producing output) using aws cli and s3 endpoints. 

Refer recently opened jira's for this HDDS-739 and HDDS-743.

With these tests, we can identify issues between direct S3 endpoint handling and AWS CLI (other tools)