OSAC-1568: Add reusable e2e workflow

[eliorerz]

Summary

• Add .github/workflows/e2e.yml — reusable workflow that boots an OpenShift clone via cluster-tool, deploys OSAC using refresh-after-snapshot.py, and runs pytest e2e tests in a container
• Secrets retrieved from local Vault via AppRole auth
• Pin actions/checkout to commit SHA with persist-credentials: false
• Clean up registry auth (auth.json) in the cleanup step

Note: The caller workflow (e2e-test.yml) will be added in PR #74 after this merges.