Migrate the hypershift-ci-python container image from UBI9 base with pip dependencies to Fedora 43 base with dnf-installed RPM packages.

Why

Using distribution-packaged Python dependencies instead of pip provides:

• Security: RPM packages go through Fedora security review and receive timely updates
• Consistency: Packages tested together as part of Fedora release
• Reproducibility: RPM versions stable within a Fedora release
• Provenance: Clear supply chain from trusted Fedora infrastructure
• Maintenance: Fedora maintainers handle dependency updates

Acceptance Criteria

• Dockerfile updated to use fedora:43 base image
• All Python dependencies installed via dnf instead of pip
• requirements.txt file removed
• Container image builds successfully
• Python imports work correctly