RHOAIENG-21668: chore(gha): securely commit encrypted subscription-manager credentials using git-crypt

```
git-crypt init
git-crypt export-key git-crypt-key
base64 git-crypt-key | gh secret set GIT_CRYPT_KEY --repo red-hat-data-services/notebook
```

Implement the security check to only allow builds for project contributors

Author: jiridanek