Handle AWS outages with allowlist skip-on-failure

[peterschmidt85]

Summary

• Add a temporary AWS region allowlist for skip-on-failure behavior
• Keep normal behavior for all other regions (fail fast on unexpected region failures)
• For allowlisted regions, skip only when the API call fails (do not pre-skip if region works)
• Log a warning only when a skip actually happens

Validation

• pre-commit run (ruff + ruff-format): passed
• ./.venv/bin/python -m py_compile src/gpuhunt/providers/aws.py: passed
• CATALOG_DIR=/Users/dstack/gpuhunt ./.venv/bin/pytest src/integrity_tests/test_aws.py -q: 3 passed