Add proxy support to Databricks connections

[Vamsi-klu]

Add explicit proxy support for Databricks connections.

What changed

This adds a documented proxies connection extra for the Databricks provider. The extra is intentionally allowlisted and only accepts http and https keys, for example:

{
  "proxies": {
    "http": "http://proxy.example.com:8080",
    "https": "http://proxy.example.com:8443"
  }
}

The configured proxy is applied to:

• Databricks REST API calls
• Databricks OAuth token exchanges
• Azure Identity token acquisition for AAD service principal and default Azure credential authentication
• Sync and async Databricks hook paths

Why

Users running Airflow behind a corporate proxy could not authenticate to Azure Databricks because token acquisition to Azure/Databricks endpoints did not receive proxy configuration.

This fixes #32576 while keeping connection extras explicit and safe. The implementation does not pass arbitrary connection extras through to client libraries; it validates and forwards only the reviewed proxies extra.

Testing

I added coverage for:

• Valid proxies parsing from Databricks connection extras
• Rejection of invalid proxy shapes and unsupported keys
• Sync Databricks REST API calls using proxies
• Async Databricks REST API calls using the matching aiohttp proxy
• AAD service principal token paths passing proxies to Azure Identity
• Databricks service-principal OAuth token exchange using proxies
• Sync and async token/API combinations
• Databricks SQL connector kwargs not receiving proxies

Commands run:

• uv run ruff format providers/databricks/src/airflow/providers/databricks/hooks/databricks_base.py providers/databricks/tests/unit/databricks/hooks/test_databricks.py providers/databricks/tests/unit/databricks/hooks/test_databricks_base.py
• uv run ruff check --fix providers/databricks/src/airflow/providers/databricks/hooks/databricks_base.py providers/databricks/tests/unit/databricks/hooks/test_databricks.py providers/databricks/tests/unit/databricks/hooks/test_databricks_base.py
• uv run ruff format providers/databricks/tests/unit/databricks/hooks/test_databricks_sql.py
• uv run ruff check --fix providers/databricks/tests/unit/databricks/hooks/test_databricks_sql.py
• uv run ./scripts/ci/prek/check_new_airflow_exception_usage.py providers/databricks/src/airflow/providers/databricks/hooks/databricks_base.py
• uv run --project providers/databricks pytest providers/databricks/tests/unit/databricks/hooks/test_databricks_base.py providers/databricks/tests/unit/databricks/hooks/test_databricks.py providers/databricks/tests/unit/databricks/hooks/test_databricks_sql.py -q

Result: 284 passed; AirflowException usage check passed.

closes: #32576

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• Yes — Codex (GPT-5)

Generated-by: Codex (GPT-5) following the guidelines

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Drafted-by: Codex (GPT-5) (no human review before posting)