aws_codebuild: Support for host kernel parameter selection setting

### Describe the feature

Given this [update](https://aws.amazon.com/about-aws/whats-new/2026/07/aws-codebuild-amazon-linux-2023/), would be great for CDK to support this natively (Cfn will need to support it first).

Boto3 currently [supports](https://docs.aws.amazon.com/boto3/latest/reference/services/codebuild/client/create_project.html) as part of the `Environment` specifier.

### Use Case

Ability to specify kernel versions dynamically is hugely beneficial for myriad use cases like performance, supporting latest functionality, etc.

### Proposed Solution

Add a parameter to `Environment`.

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### AWS CDK Library version (aws-cdk-lib)

2.257.0

### AWS CDK CLI version

2.1124.1 (build 791408c)

### Environment details (OS name and version, etc.)

Linux Fedora44

Start with the CodeBuild Environment construct and the CloudFormation support it depends on, then compare the requested setting with the Environment fields in the linked boto3 create_project documentation. Done means the host kernel parameter can be configured natively through CDK after the required Cfn support is available.

Written by the indexing model from the issue text.