Add integration test workflow

[VarshaRagavendran]

Issue #, if available:
N/A

Description of changes:
Adds a GitHub Actions workflow that runs end-to-end integration tests against a real AWS Elastic Beanstalk
environment. The workflow:

• Triggers on PR approval or manual dispatch
• Builds the action from source, then exercises the create and update deployment paths against a live EB
  environment
• Dynamically resolves the latest Python solution stack to avoid deprecation
• Uses OIDC for AWS authentication
• Cleans up all AWS resources (environment + application) on every run, even on failure
• Uses concurrency groups to prevent parallel runs from corrupting EB state

Successful run: https://github.com/VarshaRagavendran/aws-elasticbeanstalk-deploy/actions/runs/22864950594/job/66329070937
Failure run (permission issues on account): https://github.com/VarshaRagavendran/aws-elasticbeanstalk-deploy/actions/runs/22865622589/job/66331508296
Failure run (broken action code):
https://github.com/VarshaRagavendran/aws-elasticbeanstalk-deploy/actions/runs/22866215807/job/66333659028

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[yuxiang-zhang]

Thanks for the PR — the workflow is well-structured with good cleanup and concurrency handling. Two suggestions below.

[yuxiang-zhang]

LGTM — clean workflow with solid cleanup, concurrency, and secret handling.