feat(pipeline): add preDeploySteps to run steps at the start of every deploy job

[LaikaN57]

What

Adds a preDeploySteps option. The steps you give it run at the start of every deploy job, before the AWS credentials step. It works the same way preBuildSteps already does for the build job.

Why

Deploy jobs run npx cdk deploy. With no npm login, npx downloads the cdk CLI straight from the public npm registry. That access is about to be blocked by a firewall in CI, so deploy jobs need to log in to AWS CodeArtifact first, and today there is no way to add a step to them.

The steps run before the credentials step because the CodeArtifact login assumes its own AWS role. Running it first lets the deploy role's credentials replace it.

Testing

• New unit test: the step appears once, in the deploy job, before Download cdk.out.
• All 49 tests pass. Existing snapshots are unchanged, so current pipelines produce the same workflow files.

🤖 Generated with Claude Code

https://claude.ai/code/session_014QPF7k3P56ZTy24Fs6cfpi