Add force option to sky down

[andylizf]

Resolve #4059

Add a --force option to the sky down command to handle services stuck in the SHUTTING_DOWN state.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• 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

[cblmemo]

I'm a little confused. #4059 says we need a --force for sky serve down but this is adding -f to sky down. Is it expected?

[andylizf]

I'm a little confused. #4059 says we need a --force for sky serve down but this is adding -f to sky down. Is it expected?

It's a typo in the original issue, but you make me realize that the semantic is indeed not clear enough so I think maybe an option named ignore-if-controller would be better?