Implement retry mechanism for pulling the reference image

The operator doesn't retry to pull the image if there's been a failure. It only prints a single time:
```
[2025-10-07T14:56:40Z ERROR operator] Failed to compute or retrieve reference values for image localhost:5000/fedora-coreos:clevis-pin: error sending request for url (https://localhost:5000/v2/fedora-coreos/manifests/clevis-pin)
``` 