Feature request: Support AWS IAM roles

[pietervincken]

As a Nextflow infrastructure maintainer.
I want to use AWS IAM roles instead of IAM users to connect to AWS resources
In order to prevent the need for long lived high privilege credentials.

Today, an IAM user is needed for using Nextflow with AWS Batch. This request is to remove that requirement by switching to IAM Roles instead. These don't require any credentials to be maintained and can be created as part of the infrastructure creation and assigned to the correct workloads.