refactor: Update login flow for UI tests

[emmaaroche]

Description

• Refactored UI tests to log in once per session and reuse authentication state across all tests, helping to reduce test execution time
• Moved conftest.py from policies/ to parent console_plugin/ directory to apply authentication to all UI test subdirectories
• Added OpenShift exposer check to skip UI tests on non-OpenShift environments (Kind/Kubernetes)
• Added console plugin installation and enablement verification with skip/fail conditions
• Added .playwright-auth/ session cache to .gitignore and .dockerignore
• Added back UI pytest marker definition to pyproject.toml

Closes #839

Verification steps

Run all UI tests to verify conftest changes don't break tests:

make ui

or

Run alll tests using the UI Container image:

docker run --rm \
    -v /tmp/ocp/kubeconfig.kua-420-2:/run/kubeconfig:ro \
    -v $(pwd)/config/settings.local.yaml:/run/secrets.yaml:ro \
    -v $(pwd)/test-run-results:/test-run-results \
    quay.io/rh-ee-eroche/testsuite-ui:unstable

[emmaaroche]

@averevki This PR addresses your comments: #850 (comment) and #850 (comment)

[averevki]

It's good improvement. Do you have any data on how faster it's making tests run? (it's okay if not :))

[emmaaroche]

Thanks @averevki, no 'official' data, but I noticed this refactor with overview tests and policy tests it takes roughly 7 mins to run whereas that was how long just policy tests alone were taking

[azgabur]

Nice 👍