Sustainability POC Add Optimization

[dmatch01]

Initial implementation of sustainability support. Includes cost plus carbon footprint optimization. To enable cost plus carbon footprint optimization launch skypilot with the command line option--optimize-cost-target=carbon_footprint.

Tested (run the relevant ones):

• [x] Code formatting: bash format.sh
• [n/a] Any manual or new tests for this PR (please specify below)
• [ ] All smoke tests: pytest tests/test_smoke.py
• [ ] Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• [ ] Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh