feat(notifications): support InputPath and InputTransformer on notification targets

[VirtueMe]

Summary

• Adds inputPath and inputTransformer as optional fields on all notification targets
• Both are passed through to the generated AWS::Events::Rule target as InputPath / InputTransformer
• Schema updated to validate the new fields

Example

notifications:
  FAILED:
    - sns: !Ref MyTopic
      inputTransformer:
        inputPathsMap:
          status: '$.detail.status'
          name: '$.detail.name'
        inputTemplate: '"State machine <name> finished with status <status>"'
    - sqs: MY_QUEUE_ARN
      inputPath: '$.detail'

Test plan

• npx mocha lib/deploy/stepFunctions/compileNotifications.test.js passes

Closes #609

🤖 Generated with Claude Code

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/serverless-operations/serverless-step-functions@698

commit: 214603f

[zirkelc]

This probably needs to be added to the README?

[VirtueMe]

Added the missing README section documenting inputPath and inputTransformer on notification targets, with a YAML example.