Add AWS CDK template (using javascript)

[dannymidnight]

This drops in a new IaC template using CDK, similar to the Terraform & Pulumi workflows.

1. Installs npm dep for subsequent steps
2. Runs cdk synth inside node docker environment
3. Block
4. Runs cdk deploy inside node docker environment

e.g.

TODO:

• [x] Add npm run test test step since that seems pretty standard for CDK projects.
• [x] Test pipeline works using a test IAM role.
• [x] Write the README