Environment does not support defaultRole

## Describe your feature request

Add support for https://aws.amazon.com/about-aws/whats-new/2024/06/default-role-codecatalyst-environments/#:~:text=With%20the%20default%20IAM%20role,where%20CodeCatalyst%20is%20generally%20available.

## Describe the solution you'd like

A default role property.

## Describe alternatives you've considered

N/A

Start with the AWS What's New announcement linked in the issue, then locate the repository's environment configuration entry point. Define the expected defaultRole property and verify it against the supported CodeCatalyst environment behavior; the issue names no file or test, so completion criteria need clarification.

Written by the indexing model from the issue text.