Add Amazon ECR source action to pipelines.CodePipelineSource class.

Use Case

Pipelines that trigger on push to Amazon ECR repository (e.g., base image update due to security CVE)

Proposed Solution

Add pipelines.CodePipelineSource.ecr(...) factory method.

Other

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

This is a 🚀 Feature Request