Add terminationGracePeriodSeconds support for PgBouncer in Helm chart

[antruigon]

The chart ships a default PgBouncer preStop hook that drains client connections for up to 120 seconds (killall -INT pgbouncer && sleep 120), but the Deployment never sets terminationGracePeriodSeconds, so the Kubernetes default of 30s SIGKILLs the pod mid-drain on a node drain or eviction and cuts in-flight client connections.

Every other long-running component in the chart (scheduler, workers, triggerer, dag-processor, statsd, redis, otel collector) already exposes this value; PgBouncer was the only one missing it, despite holding the database connections of all the others.

This adds pgbouncer.terminationGracePeriodSeconds, defaulting to 120 to match the preStop drain window. PgBouncer exits as soon as the last client connection is released, so the value is an upper bound rather than a fixed wait. Deployments that prefer the previous behaviour can set it back to 30.

Covered by a parametrized test in test_pgbouncer.py (default and override).

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

• Yes — Claude Code (Claude Fable 5)

Generated-by: Claude Code (Claude Fable 5) following the guidelines

[boring-cyborg]

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[Miretpl]

Could you please match the PR description with the project template and follow https://github.com/apache/airflow/blob/main/contributing-docs/05_pull_requests.rst#gen-ai-assisted-contributions?

[antruigon]

Done, sorry for the miss. The description now follows the project template and includes the Gen-AI disclosure. The change was AI-assisted and reviewed by me. I validated the rendered chart and ran the helm tests locally (test_pgbouncer.py, test_pdb_pgbouncer.py, test_chart_quality.py) before pushing