Add fusion regression

[Stefan824]

This PR should address issue #2595 if goes well.

• Added a new script run_fusion_regression.py to handle fusion regression tasks. It behaves similarly to run_regression.py.
• Included two test yaml files.
• Tests could be performed following anserini/docs/fuse-regressions/test-setup.md.
• Next steps in mind are
  • Implementing an auto-script to generate more yaml files for fusion based on current regression yamls (working on it)
  • Doing experiments to find out expected eval results for fusion on different runs with different fusion methods and parameters