Support for applications running on Kubernetes

[thiagosalvatore]

We’ve been using AioDynamo for a while in my current company. The existing credentials work pretty well with ECS and EC2 machines. However, when running inside a Kubernetes cluster (like EKS), the metadata from the EC2 instance is not available and we don’t have the credentials from AWS as environment variables because our pod basically assumes a role on AWS. We also don’t have a file with credentials or anything like that. That said, we needed a way to fetch the credentials from AWS that our pod has, and luckily AWS offers us a way to do that by calling get_credentials.

I opened a PR with the fix that we've been using here for a while now:
#127