[Storage] Make s3 bucket creation log visible to the users

[landscapepainter]

This resolves #3729 with some refactoring.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Smoke tests pytest tests/test_smoke.py::TestStorageWithCredentials --aws
• manual sky launch with the task yaml mentioned in [Storage] creating s3 bucket fails to display log to user #3729:

$ sky launch test.yaml --cloud gcp -y
Task from YAML spec: test.yaml
I 07-06 21:59:14 storage.py:1380] Created S3 bucket no-log-s3-creation in us-east-1
I 07-06 21:59:18 storage.py:1824] Created GCS bucket log-gcs-creation in US with storage class STANDARD
I 07-06 21:59:22 optimizer.py:695] == Optimizer ==
I 07-06 21:59:22 optimizer.py:706] Target: minimizing cost
I 07-06 21:59:22 optimizer.py:718] Estimated cost: $0.4 / hour
I 07-06 21:59:22 optimizer.py:718]
I 07-06 21:59:22 optimizer.py:843] Considered resources (1 node):
I 07-06 21:59:22 optimizer.py:913] ----------------------------------------------------------------------------------------------
I 07-06 21:59:22 optimizer.py:913]  CLOUD   INSTANCE        vCPUs   Mem(GB)   ACCELERATORS   REGION/ZONE     COST ($)   CHOSEN
I 07-06 21:59:22 optimizer.py:913] ----------------------------------------------------------------------------------------------
I 07-06 21:59:22 optimizer.py:913]  GCP     n2-standard-8   8       32        -              us-central1-a   0.39          ✔
I 07-06 21:59:22 optimizer.py:913] ----------------------------------------------------------------------------------------------
I 07-06 21:59:22 optimizer.py:913]
Running task on cluster sky-xxxx-gcpuser...
I 07-06 21:59:22 cloud_vm_ray_backend.py:4411] Creating a new cluster: 'sky-xxxx-gcpuser' [1x GCP(n2-standard-8)].
I 07-06 21:59:22 cloud_vm_ray_backend.py:4411] Tip: to reuse an existing cluster, specify --cluster (-c). Run `sky status` to see existing clusters.
I 07-06 21:59:25 cloud_vm_ray_backend.py:1406] To view detailed progress: tail -n100 -f /home/gcpuser/sky_logs/sky-2024-07-06-21-59-20-661208/provision.log
I 07-06 21:59:27 provisioner.py:76] Launching on GCP us-central1 (us-central1-a)
I 07-06 22:00:27 provisioner.py:458] Successfully provisioned or found existing instance.
I 07-06 22:01:14 provisioner.py:560] Successfully provisioned cluster: sky-xxxx-gcpuser

[cblmemo]

Thanks for the fix! LGTM.