Add support for iam roles for service accounts in AWS

[adamjohnson01]

Due to this issue in the aws sdk, it is not possible to authenticate using iam roles for service accounts in AWS EKS.

This is because session.New is being used.

cortex/pkg/chunk/aws/s3_storage_client.go

Line 54 in 4a7f5b0

s3Client := s3.New(session.New(s3Config))

session.New is deprecated and requires the AWS_SDK_LOAD_CONFIG environment variable to be set in order to automatically call AssumeRoleWithWebIdentity.

I propose updating to use session.NewSession instead. I am happy to contribute this change.

[bboreham]

Thanks for pointing this out. Please go ahead and make a PR if you are able.
Do we need to change this too?

cortex/pkg/chunk/aws/dynamodb_storage_client.go

Line 847 in 4a7f5b0

return dynamodb.New(dynamoDBSession), nil

[adamjohnson01]

Yes, that need to change as well.