[Cudo] Handle missing project errors

[JungleCatSW]

When a user attempted to use skypilot without a project being set in the credentials file (cudo.yml) it threw an error.

1. Now the instructions have been updated to tell users to create a project.
2. 1. On sky check it checks for a valid project and instructs on how to create one if it isn't found.
3. All other uses of project throw an error with a useful message if somehow a user still doesn't have a valid project.

Tested (run the relevant ones):

• [x ] 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: bash tests/backward_comaptibility_tests.sh

[Michaelvll]

Thank you for the quick fix @JungleCatSW! LGTM.