CodeBuild: Custom Lambda Images

### Describe the feature

CDK with AWS Lambda compute in AWS CodeBuild does not currently support Custom Images from ECR.

### Use Case

Currently there is demand to use Lambda as a build environment for CodeBuild. However the Curated images don't cover every use case and the need for a custom image for Lambda compute is needed.

This is currently supported within the Console and is only not supported in CDK.

### Proposed Solution

We need to expand our implementation to support custom images and not just the curated images. The functionality should match that of the console. Custom Image -> Lambda -> Linux or Arm -> ECR -> Image.

### Other Information

Currently the only ask is that the we can match what is available in the console.

Currently the documentation states there is no support for this.

https://docs.aws.amazon.com/cdk/api/v2/python/aws_cdk.aws_codebuild/README.html

### Acknowledgements

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

### CDK version used

2.139

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

Linux

Start with the CodeBuild README linked in the issue, then locate the CDK CodeBuild entry point for Lambda compute and its image configuration. Compare the supported options with the console flow: Custom Image, Lambda, Linux or Arm, ECR, and Image. Done means CDK supports that custom ECR image path and the documentation no longer says it is unsupported.

Written by the indexing model from the issue text.