Add migration for the new aws-config setting generator

[ginglis13]

Issue number:

n/a

Description of changes:

Add migration for the new aws_config setting generator.

Testing done:

Upgrade, non FIPS AMI, `settings.aws.config` null:

bash-5.1# apiclient get os

bash-5.1# apiclient get settings.aws
{
  "settings": {
    "aws": {
      "profile": "default",
      "region": "us-west-2"
    }
  }
}

After upgrade:

bash-5.1# apiclient get os

bash-5.1# apiclient get settings.aws
{
  "settings": {
    "aws": {
      "config": "W2RlZmF1bHRdCnVzZV9maXBzX2VuZHBvaW50PWZhbHNl",
      "profile": "default",
      "region": "us-west-2"
    }
  }
}

Downgrade (the setting remains):

bash-5.1# apiclient get settings.aws
{
  "settings": {
    "aws": {
      "config": "W2RlZmF1bHRdCnVzZV9maXBzX2VuZHBvaW50PWZhbHNl",
      "profile": "default",
      "region": "us-west-2"
    }
  }
}

Upgrade, non FIPS AMI, `settings.aws.config` already set:

``` bash-5.1# apiclient get os

bash-5.1# apiclient get settings.aws
{
"settings": {
"aws": {
"config": "W2RlZmF1bHRdCnJldHJ5X21vZGU9c3RhbmRhcmQK",
"profile": "default",
"region": "us-west-2"
}
}
}

After upgrade:

bash-5.1# apiclient get os

bash-5.1# apiclient get settings.aws
{
"settings": {
"aws": {
"config": "W2RlZmF1bHRdCnJldHJ5X21vZGU9c3RhbmRhcmQK",
"profile": "default",
"region": "us-west-2"
}
}
}

Downgrade (the setting remains):

bash-5.1# apiclient get settings.aws
{
"settings": {
"aws": {
"config": "W2RlZmF1bHRdCnJldHJ5X21vZGU9c3RhbmRhcmQK",
"profile": "default",
"region": "us-west-2"
}
}
}

</details>

**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.

[bcressey]

Changes LGTM once we're ready with the core kit release.