show logs for storage mount

[zpoint]

Feature for #4105

• A global logger, initialized as a singleton on the first call, bound to a temporary log file.
• All storage object uploads will use this logger to log the corresponding output.

(sky) zepingguo@WIN11-JHL:~/skypilot$ cat ~/hello_sky/work_dir_1.yaml 
name: test_workdir_bucket_name_1

workdir: .

resources:
  cloud: azure

file_mounts:
  # this will use the user config
  /checkpoint:
    name: zpoint-filemounts-bucket
    source: ~/tmp/dir1
    mode: MOUNT
    store: azure

  /dir1: ~/tmp/dir1
  /dir2: ~/tmp/dir2
  /dir3/dir3.py: ~/tmp/dir1/dir1.py
run: |
  for i in {1..5}; do
    echo "Hello, SkyPilot World! $(date)"
    touch /checkpoint/$i.txt
  done
(sky) zepingguo@WIN11-JHL:~/skypilot$ 

sky jobs launch ~/hello_sky/work_dir_1.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_fill_in_the_name
• [ ] Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh