[AWS] Support capacity block reservation

[Michaelvll]

Blocked by #3852.

This PR adds support for capacity block reservations.

We are not able to test it at the moment due to the lack of quota for creating a capacity block.

Thanks a lot to @jasonkrone for the awesome instruction PR: https://github.com/skypilot-org/skypilot/pull/3818/files

Also, thanks Sherjil for helping us test this PR on real capacity block.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
  • A user tested it with their capacity block on f693555, and it seems working.
• 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

[Michaelvll]

@cblmemo This is ready for a review.

[cblmemo]

Thanks for adding this feature @Michaelvll ! LGTM