moving to gradle build system

[samuel-oci]

Description

• Moving this repository to gradle to be consistent with standard plugins.
• Upgrade OpenSearch and SDK versions
• Move to async SDK client to address bug in SDK that caused unrecoverable timeouts during snapshots and flakey testing
• Minor bug fix in object storage fixture

Issues Resolved

List any issues this PR will resolve, e.g. Closes https://github.com/opensearch-project/opensearch-oci-object-storage/issues/20.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.