cdk-assets: private ecr registry support overwrite any additional docker configuration

[gyalai-aws]

Describe the bug

• We have a proxy configuration for docker in the ./docker/config.json file.
• We are using private ecr to fetch our images which configuration is placed into the ~/.cdk/cdk-docker-creds.json file

The cdk-assets creates a new docker config file but it is only placing the contents of the ~/.cdk/cdk-docker-creds.json file and only the credHelpers property, so it is not even possible to include the proxy settings.

Expected Behavior

Both configuration should be respected.

Current Behavior

Only credentials are kept.

Reproduction Steps

see before.

Possible Solution

Change this line: https://github.com/aws/aws-cdk/blob/1fcef6309e54d7ec1e179c22a47a235b38fa1673/packages/cdk-assets/lib/private/docker.ts#L168C81-L168C92

Options:

1. Write out the whole ~/.cdk/cdk-docker-creds.json file not just the credHelpers
2. Add support to include additional ~/.cdk/cdk-docker*.json files to plug in additional docker configurations
3. Check whenever a ~./docker/config.json file exists and merge both files.

Additional Information/Context

No response

CDK CLI Version

2.147.0

Framework Version

No response

Node.js Version

Any

OS

Any

Language

TypeScript

Language Version

No response

Other information

No response

[khushail]

Thanks @gyalai-aws for reporting this and submission of PR.