Thanos OSS(Aliyun) provider does not support IAM(RAM) role

[feiyunzhou]

The AWS provider supports to assume AWS IAM role to use S3, but Aliyun OSS provider does not support IAM(RAM) role.

We can find the code for AWS provider here https://github.com/thanos-io/objstore/blob/main/providers/s3/s3_aws_sdk_auth.go, but the Aliyun OSS provider does not have it.

Aliyun has GO sdk for assume role and get the STS token, here https://github.com/AliyunContainerService/ack-ram-tool/tree/main/examples/rrsa/go-sdk

[yeya24]

Thanks for the report. I think none of the Thanos maintainers use Aliyun OSS object store. If you want this feature, feel free to pick it up and create a PR. We are happy to accept it!