Expose plan monitor report paths

[wayyoungboy]

Summary

• print the generated SQL plan monitor HTML report path and resources directory
• return report_file and resources_dir in the gather result data alongside store_dir
• add unit coverage for the result path payload

Fixes #1011

Verification

• PYTHONPATH=. python -m pytest test/gather/test_gather_plan_monitor.py test/common/test_scene.py -q
• black --check -S -l 256 src/handler/gather/gather_plan_monitor.py test/gather/test_gather_plan_monitor.py
• python workflow_data/check_py_files.py .
• git diff --check