[Azure][Disk] Ultra tier on Azure with disk bursting.

[cblmemo]

This PR adds ultra tier on Azure, leveraging Azure disk bursting.

Since configure the disk bursting requires restarting the VM, which introduces ~44s overhead to the provisioning stage, we still set the best disk tier to high on Azure for now. We should investigate the attached data disk which could support Premium SSD v2 & ultra disk.

I 09-13 14:20:25 instance.py:306] Stopped instances to enable disk bursting in 23.10 seconds.
I 09-13 14:20:37 instance.py:318] Enabled disk bursting for {len(disks)} disks in 12.44 seconds.
I 09-13 14:20:46 instance.py:324] Started instances to enable disk bursting in 8.56 seconds.

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 ultra --disk-size 1024 launches successfully.
  • sky launch --cloud azure --disk-tier ultra outputs error Azure Ultra SSD requires a disk size greater than 512GB.
• 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

[github-actions]

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