aws-ecr-assets: support for .containerignore file and / or alternative ignore file

### Describe the feature

Podman supports two different ignore file variants: `.dockerignore` (for compatibility reasons) and `.containerignore`, see https://docs.podman.io/en/stable/markdown/podman-build.1.html#files. Moreover, it's possible to provide alternative ignore file.

But, `.dockerignore` file name is hardcoded in aws cdk:
https://github.com/aws/aws-cdk/blob/aebb331e60b736969f5bccbf5b427e11dc5fc997/packages/aws-cdk-lib/aws-ecr-assets/lib/image-asset.ts#L454

### Use Case

.containerignore natively supported by Podman is ignored by aws cdk, which force me to rename file or use include / exclude properties.

### Proposed Solution

To add ability to specify alternative ignore file (as it already implemented for Dockerfile itself), and / or support vendor-free file names by default (Containerfile / .containerignore).

### Other Information

_No response_

### Acknowledgements

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

### CDK version used

2.178.2

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

mac os

Start in packages/aws-cdk-lib/aws-ecr-assets/lib/image-asset.ts at the hardcoded .dockerignore handling, and compare it with the existing Dockerfile selection behavior. Clarify whether the change should support an explicitly selected ignore file, .containerignore by default, or both; done means the chosen behavior works for Podman-compatible builds without requiring renaming or include/exclude workarounds.

Written by the indexing model from the issue text.