Use role defaults for container images in IOP tests

[ehelms]

Why are you introducing these changes? (Problem description, related links)

IOP tests hardcoded container image references (e.g. quay.io/iop/host-inventory:latest), which meant they could drift out of sync with the actual images configured in role defaults. If the image or tag changed in deployment configuration, the tests would still use the old values.

What are the changes introduced in this pull request?

• Add a shared iop_image pytest fixture in tests/iop/conftest.py that reads container_image and container_tag from each role's defaults/main.yaml
• Replace all hardcoded quay.io/iop/* image references across test_advisor.py, test_ingress.py, test_integration.py, and test_inventory.py with calls to the iop_image fixture

How to test this pull request

Steps to reproduce:

• Deploy an IOP environment and run the IOP test suite: python -m pytest tests/iop/ -vv
• Verify that the container images used in test podman run commands match the values from the corresponding role defaults under src/roles/

Checklist

• Tests added/updated (if applicable)
• Documentation updated (if applicable)