Add support for AWS_PROFILE Environment Variable

## Community Note

Please vote on this issue by adding a 👍 reaction to the original issue to help the community and maintainers prioritize this request. Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request. If you are interested in working on this issue or have submitted a pull request, please leave a comment.

### Tell us about your request

I would like to utilize the environment variable `AWS_PROFILE` to set my AWS profile.

### Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?

I am trying to solve two problems:

1. If I set the `AWS_PROFILE` this sets my profile for the AWS CLI and a number of other libraries - this is so common that I expect many AWS customers to use that variable with using the be cli tool as well.
2. Ensuring a consistent user experience across all AWS provided tooling

### Are you currently working around this issue?

Yes.

### How are you currently solving this problem?

I need to remember to use the `--profile` option when using this particular tool.

### Additional context

Anything else we should know?

### Attachments

If you think you might have additional information that you'd like to include via an attachment, please do - we'll take a look. (Remember to remove any personally-identifiable information).

Start by locating the EB CLI handling for the `--profile` option and trace how the selected AWS profile is passed through commands. Add support for `AWS_PROFILE` as the default when `--profile` is not supplied, then verify that the environment variable selects the expected profile consistently.

Written by the indexing model from the issue text.