Support for IAM role-based authentication in AWS ECR registries

## Motivation  

[Why is this Task important? Explain the context and reasons for this task.]  

- Currently, in order to use AWS ECR as a registry in [http://Backend.AI](http://Backend.AI) , you need to use access_key, secret_key.
However, when using [http://Backend.AI](http://Backend.AI) within AWS, it is more secure to authenticate in the same way as an iam role.

## Objective  

[Clearly state the purpose or goal of this task.]  

- Support for using the iam role method of authentication when using AWS ECR as a registry.

## Details  

[Outline the specific steps or changes needed to complete this task.]  

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## Impact  

[Describe how this task may indirectly influence other services, if at all.]  

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JIRA Issue: BA-1120