Improve airflowctl required field validation

[bobu-putheeckal]

Improve airflowctl client-side validation for API request bodies so missing required generated Pydantic fields are reported clearly before building/sending requests.

Changes:

• Add a reusable required-field validator using Pydantic field is_required().
• Validate generated request body models before dumping them for API requests.
• Reuse the validator while importing pools, variables, and connections from JSON so missing API-required fields point to the specific missing input.
• Add focused tests for direct API operations and import commands.

Closes: #57721

Tests:

• uv run --project airflow-ctl ruff check airflow-ctl/src/airflowctl/api/operations.py airflow-ctl/src/airflowctl/ctl/cli_config.py airflow-ctl/src/airflowctl/ctl/commands/connection_command.py airflow-ctl/src/airflowctl/ctl/commands/pool_command.py airflow-ctl/src/airflowctl/ctl/commands/variable_command.py airflow-ctl/src/airflowctl/exceptions.py airflow-ctl/tests/airflow_ctl/api/test_operations.py airflow-ctl/tests/airflow_ctl/ctl/commands/test_connections_command.py airflow-ctl/tests/airflow_ctl/ctl/commands/test_pool_command.py airflow-ctl/tests/airflow_ctl/ctl/commands/test_variable_command.py
• uv run --project airflow-ctl pytest airflow-ctl/tests

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Was generative AI tooling used to co-author this PR?

• Yes (OpenAI Codex)

Generated-by: OpenAI Codex

[potiuk]

@bobu-putheeckal A few things need addressing before review — see our Pull Request quality criteria.

• ❌ Static checks fail: CI image checks / Static checks. See the Checks tab.

No rush.

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Note: This comment was drafted by an AI-assisted triage tool and may contain mistakes. Once you have addressed the points above, an Apache Airflow maintainer — a real person — will take the next look at your PR. We use this two-stage triage process so that our maintainers' limited time is spent where it matters most: the conversation with you.

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Drafted-by: Claude Code (Opus 4.7); reviewed by @potiuk before posting

[bobu-putheeckal]

Pushed 6bf4de8d6e to address the ruff format static-check failure. The current PR check rollup no longer shows CI image checks / Static checks failing.

[kaxil]

PR template hasn't been followed on any of your PRs. As such I am closing all your PRs since I see little to no evidence of actual testing and mass PRs to Airflow & other repos.