Replaced all instances of gsutil with gcloud

[kvo3]

Summary

• Replace all gsutil CLI calls with gcloud storage equivalents across production code, tests, docs, and examples, in preparation for gsutil deprecation
• Translate gsutil-specific flags to their gcloud equivalents
• Rename internal bash functions and Python constants
• Bump version to 0.5.3.dev0
• Updated: All integration tests and test utilities to use gcloud storage commands
• Updated README.md, docs/code.md, docs/providers/README.md, and all example READMEs/scripts to reference gcloud storage commands and link to the gcloud storage docs
• Bump Cloud SDK Docker image from 294.0.0-slim to 499.0.0-slim since gcloud storage requires SDK >= 407
• Updated examples folder to use google-batch instead of google-cls-v2 due to the deprecation of the latter

Production code changes

• google_utils.py: Rewrote gcloud_cp() and gcloud_rsync() bash helper functions with gcloud storage syntax and
  translated flag formats. Updated LOCALIZATION_LOOP and DELOCALIZATION_LOOP to call the renamed functions.
• local.py: Updated _localize_inputs_command(), _delocalize_outputs_commands(), and _delocalize_logging_command() to use gcloud storage cp with --billing-project instead of gsutil -u ... -mq cp.
• providers_util.py: Changed _LOCALIZE_COMMAND_MAP[P_GCS] from gsutil -m rsync -r to gcloud storage rsync -r.
• google_batch.py / google_v2_base.py: Updated template variable references to use renamed constants.

Example code changes

• --provider google-cls-v2 → --provider google-batch
• --zones "us-central1-*" → --regions us-central1 (google-batch doesn't expand zone wildcards)

Test code changes

• Updated all integration test scripts and Python test utilities to use equivalent gcloud storage commands
• Updated test_util.py functions naming: gsutil_ls_check() to gcloud_ls_check(), gsutil_cat() to gcloud_cat()
• Updated retry config in script_block_external_network.sh: gsutil -o 'Boto:num_retries=0' to --retry-max-attempts=0
• Updated e2e_io_recursive.sh sed pattern from s#/:$## to s#/$## to match gcloud storage ls directory marker format
• Removed obsolete pass_credentials_to_gsutil diagnostic line from test_setup_e2e.sh

Documentation changes

• Updated README.md, docs/code.md, docs/providers/README.md, and all example READMEs and scripts
• Updated links from gsutil docs to gcloud storage reference docs
• Updated commands: gsutil mb to gcloud storage buckets create, gsutil iam ch to gcloud storage buckets
  add-iam-policy-binding

BENCH-9580

[PeterSu92]

TLDR two breaking issues identified, one around the local-provider breaking for non GCS input/output (gcloud storage cp doesn't work for local files), another for the retry-disable flag. Another comment is more on drift and shouldn't block PR merge, but should be addressed nonetheless

[PeterSu92]

LGTM - non-blocking ask, could you add .ipynb_checkpoints/ to .gitignore?