Added support for throwing errors from CDK stack metadata

[karakter98]

These changes allow tools like cdk-nag to cause runtime errors when running the Pulumi program by attaching errors and warnings as metadata to the CDK cloud assembly.

Before, using cdk-nag in a Pulumi program would not print the error messages to the console, and the pulumi up command could go through even if cdk-nag checks were failing.

This PR added dependencies, because it uses the CDK CLI package to parse the stack metadata and emit the errors/warnings. The aws-cdk-lib package lacks this functionality.

Closes #86

[github-actions[bot]]

PR is now waiting for a maintainer to run the acceptance tests. This PR will only perform build and linting. Note for the maintainer: To run the acceptance tests, please comment /run-acceptance-tests on the PR

[github-actions[bot]]

PR is now waiting for a maintainer to run the acceptance tests. This PR will only perform build and linting. Note for the maintainer: To run the acceptance tests, please comment /run-acceptance-tests on the PR