aws-ecr-assets: skip docker build with parameter

### Describe the feature

I want to be able to skip the docker build with a parameter. Something like this:
```
import { DockerImageAsset } from "aws-cdk-lib/aws-ecr-assets";

...

new DockerImageAsset(scope, "AppDockerImage", {
directory: path.join(__dirname, "../"),
skipBuild: process.env.SKIP_BUILD,
});
```

### Use Case

Sometimes I just changed something in the infrastructure and want to test the changes without needing to rebuild the docker image since it may take very long. For that, I would like to have a flag in the pipeline that sets an environment variable. That variable can be used to skip the docker build.

### Proposed Solution

See feature description

### Acknowledgements

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

### CDK version used

2.79.1

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

macOS

Start at the DockerImageAsset entry point in aws-ecr-assets and trace how the current Docker build is triggered. Define the parameter's behavior for the infrastructure-only workflow, including what happens when the build is skipped, and verify that the requested pipeline use case works without rebuilding the image.

Written by the indexing model from the issue text.