add -o json option to cost-report

[MaxVanDijck]

adds a -o json output for the cost-report cli to address #9499 (comment)

Added unittests for the new json output which are similar to the other unittests for json output

Tested (run the relevant ones):

• Code formatting: install pre-commit (auto-check on commit) or bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: /smoke-test (CI) or pytest tests/test_smoke.py (local)
• Relevant individual tests: /smoke-test -k test_name (CI) or pytest tests/test_smoke.py::test_name (local)
• Backward compatibility: /quicktest-core (CI) or pytest tests/smoke_tests/test_backward_compat.py (local)

[gemini-code-assist]

Code Review

This pull request implements JSON output support for the sky cost-report command, including the necessary CLI flag and logic to format cluster records as JSON. It also adds comprehensive unit tests to verify the new functionality. Review feedback suggests moving a pylint suppression comment to the correct parameter and providing a default value for the output_format argument to ensure consistency when the function is called programmatically.

[Michaelvll]

Thanks for the contribution @MaxVanDijck! It looks mostly good to me, except for the resource output format (see comment below)