add aws-creds settings defaults to all AWS variants

[ginglis13]

Issue number:

Related: #1667

Description of changes:

The aws-ecs-* and aws-dev variants do not include the aws-creds settings defaults by default. Add these settings as defaults for these variants. This ensures that these corresponding FIPS variants will include the changes from #4268 and
bottlerocket-os/bottlerocket-core-kit#218

Testing done:

Launch each variant affected by this change, ensure settings.aws appears as expected.

[ssm-user@control]$ apiclient get settings.aws
{
  "settings": {
    "aws": {
      "profile": "default",
      "region": "us-west-2"
    }
  }
}

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.