[Storage] Add region argument for AWS s3 upload command

[Michaelvll]

In some of AWS regions, such as eu-south-1, --region has to be provided to upload to those regions.

Fixes #3405

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
  • sky launch --cloud aws --region us-west-2 test.yaml --env STORAGE_NAME=test-s3-zhwu-us-west-2
  • sky launch --cloud aws --region us-east-1 test.yaml --env STORAGE_NAME=test-s3-zhwu-us-east-1
  • sky launch --cloud aws --region eu-south-1 test.yaml --env STORAGE_NAME=test-s3-zhwu-eu-south-1
  • sky launch --cloud aws --use-spot test.yaml --env STORAGE_NAME=test-s3-zhwu-spot (goes to eu-south-1 by default)
  • sky launch --cloud aws test.yaml --env STORAGE_NAME=test-s3-zhwu-on-demand (goes to us-east-1 by default)

  envs:
    STORAGE_NAME:
  
  file_mounts:
    /dst:
      name: $STORAGE_NAME
      source: examples
      mode: MOUNT
  
  resources:
    cloud: aws
    cpus: 2
  
  run: |
    ls -al /dst | grep tpu
  

• 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]

This is still problematic for sky jobs launch, due to not specifying region in places, such as
https://github.com/skypilot-org/skypilot/blob/master/sky/cloud_stores.py#L49-L69

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[github-actions]

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