[Core][Disk] High disk tier on Azure

[cblmemo]

Added a high disk tier for Azure. The new tier uses P50 on Premium_LRS.

Discussions

• For disk size >= 4096, it will automatically select P50 and this does not make any difference b/t medium and high tier.
• Investigate if update the disk performance can be done on python API.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
  • sky launch --cloud azure --disk-tier high and manually check the console
• 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]

Thanks for the quick support of high disk tier for Azure @cblmemo! Several comments.