[OCI] Set default image to ubuntu LTS 22.04

[HysunHe]

Set the default image for both GPU and CPU to ubuntu 22.04.

Please also help review the catalog PR skypilot-org/skypilot-catalog#107

All images are validated with the following passed tests:
test1: sky launch -c gpu-2204 examples/oci/gpu-ubuntu-2204.yaml (GPU ubuntu 22.04)
test2: sky launch -c gpu-ol9 examples/oci/gpu-oraclelinux9.yaml (GPU oraclelinux9)
test3: sky launch -c gpu-ol8 hysun_sky.yaml --image-id skypilot:gpu-oraclelinux8 (GPU oraclelinux8)
test4: sky launch -c gpu-2204 examples/oci/gpu-ubuntu-2204.yaml (comment out the image_id for testing the gpu default image)
test5: sky launch -c cputest --cloud oci --region us-sanjose-1 uptime (CPU default image: ubuntu 22.04)
test6: sky launch -c cputest --cloud oci --region us-sanjose-1 --image-id skypilot:cpu-oraclelinux8 "cat /etc/os-release" (CPU oraclelinux8)
test7: sky launch -c cputest --cloud oci --region us-sanjose-1 --image-id skypilot:cpu-oraclelinux9 "cat /etc/os-release" (CPU oraclelinux9)

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

[HysunHe]

@cblmemo @Michaelvll . Minor change: just add the latest oci gpu image (NVIDIA GPU-Optimized VMI) to the catalog file. And set the default gpu image to this one in oci config. Request your review for this.

[cblmemo]

Thanks for adding this @HysunHe ! Mostly lgtm. Left a discussion on the catalog PR ;)

[cblmemo]

Thanks @HysunHe ! LGTM.