[platform] Add support for using an IAM instance profile, instead of provisioned AWS API keys.

## Tell us about the problem you're trying to solve
We are trying to deploy airbyte, in AWS, without provisioning any additional AWS API keys.

## Describe the solution you’d like
I would like Airbyte to support using IAM instance profile, like most software.

The AWS SDK already knows how to automatically use the IAM instance profile - you only have to _not_ pass any credentials to it - and it will search for credentials in multiple ways.

## Describe the alternative you’ve considered or used
We don't have an alternative, as provisioning API keys for service accounts is against our existing security posture.

## Additional context
Add any other context or screenshots about the feature request here.

## Are you willing to submit a PR?
I am willing to submit a PR, if somebody can point me to the relevant places in the code that create AWS API clients.