(aws-cdk-cli): Improve error message when 'CDK_DOCKER' environment variable is set

[dineshb514]

Describe the bug

aws-cdk-cli/packages/cdk-assets/lib/private/docker.ts

Line 229 in a3b9762

"Unable to execute 'docker' in order to build a container asset. Please install 'docker' and try again.",

when CDK_DOCKER is set to custom command or to another agent, please improve the error messaging to the right agent.
ref::

aws-cdk-cli/packages/cdk-assets/lib/private/docker.ts

Line 310 in a3b9762

return process.env.CDK_DOCKER ?? 'docker';

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

No response

Expected Behavior

When CDK_DOCKER environment variable is set, error message should be

'Unable to execute 'value of CDK_DOCKER' in order to build a container asset. Please install 'CDK_DOCKER' and try again'

Current Behavior

Even though CDK_DOCKER environment variable is set, error message still shows as

'Unable to execute 'docker' in order to build a container asset. Please install 'docker' and try again'

Reproduction Steps

Set environment variable 'CDK_DOCKER' to podman, and transfer image assets.

Possible Solution

Unable to execute '${getDockerCmd()}' to build a container asset. Please install '${getDockerCmd()}' and try again.,

Additional Information/Context

No response

CDK CLI Version

latest

Framework Version

No response

Node.js Version

current

OS

All

Language

TypeScript

Language Version

No response

Other information

No response

[pahud]

Thank you. This makes sense to me. Feel free to submit a PR and the maintainer will help you address it.