[OCI] Support OCI Object Storage

[HysunHe]

This is the implementation of the OCI Object Storage store (Re-submit).

It is an usually solid requirement for those using SkyPilot with OCI, otherwise user has to enable other supported cloud (with buckets) to leverage its cloud storage for data sync, for example, sky serve require cloud storage to sync workdir.

Actually I have implemented and used the OCI Object Storage with SkyPilot quite a long time (mainly for POC projects), now submit the PR to merge the code to the repo because there are requirements from other users.

For documentation to add OCI store, we can do it later after this PR.

sky launch -y -c smoke_test --cloud oci --num-nodes 2 examples/oci/oci-mounts.yaml

Tested (run the relevant ones):

• 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_oci_mounts
• Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh

[HysunHe]

@Michaelvll @cblmemo Hi Zhanghao & Tianxia, Ask for your support to review/someone else to review the PR. Thanks.

[cblmemo]

Thanks for this amazing work @HysunHe ! Left some discussions :))

[HysunHe]

@cblmemo Thanks for the prompt review. All points are addressed.