Use POST for integration add-multiple commands

[Rohithmatham12]

Summary

• switch generated add-multiple integration commands from PUT to POST for configuration creation endpoints
• keep AWS unchanged because its command already has separate add/update semantics
• align add-multiple valid-input tests with the POST behavior already expected by the basic add-multiple tests

Fixes #140.

Testing

• CORTEX_BASE_URL=http://localhost CORTEX_API_KEY=test POETRY_CACHE_DIR=/private/tmp/cortexapps-cli-poetry-cache poetry run pytest tests/test_integrations_*.py -k add_multiple -q