Add user agent to AWS CLI requests

[clareliguori]

Setting the user agent for the AWS CLI helps provide more context in AWS CloudTrail entries about the API calls made by the Porter AWS mixin, especially where Porter might be using the same credentials used by other tools.

Example CloudTrail entry snippet for an S3 CreateBucket API call using the aws-bucket example, showing the Porter user agent:

{
    "eventVersion": "1.08",
    "eventTime": "2022-09-07T15:37:18Z",
    "eventSource": "s3.amazonaws.com",
    "eventName": "CreateBucket",
    "awsRegion": "us-east-1",
    "userAgent": "[aws-cli/2.7.29 Python/3.9.11 Linux/5.15.0-46-generic exec-env/getporter/porter getporter/aws/v0.0.0 exe/x86_64.debian.9 prompt/off command/s3api.create-bucket]",

[carolynvs]

This is super helpful, thank you! 💯

[carolynvs]

Thanks for the PRs, @clareliguori! I would love to connect and hear about how it's going so far using Porter with AWS. I'm always looking for more ways to make the mixins more useful and work on all clouds. If you are interested in sharing your experience, my email is me@carolynvanslyck.com.