WPB-24882 improve connection pool management

[battermann]

https://wearezeta.atlassian.net/browse/WPB-27400

Checklist

• Add a new entry in an appropriate subdirectory of changelog.d
• Read and follow the PR guidelines

[Copilot]

Pull request overview

This PR (WPB-26489) updates Arbiter integration to improve PostgreSQL connection pool management by ensuring background-worker job execution uses the shared Hasql pool (and avoids dedicating extra long-lived connections), alongside an Arbiter dependency bump and related API adjustments.

Changes:

• Switch background-worker Arbiter workers to a pool-backed, poll-only execution model (no LISTEN/NOTIFY listener connection; shared Hasql pool for DB work).
• Move/centralize Arbiter migration connection-string construction into wire-subsystems (mkArbiterConnectionString) and update services to use it.
• Update Arbiter-related types/APIs (e.g., JobRegistry definition) and align Nix/Cabal deps plus operator documentation/changelog.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
services/galley/src/Galley/Run.hs	Uses mkArbiterConnectionString for Arbiter migrations; keeps Hasql pool usage unchanged.
services/background-worker/src/Wire/BackgroundWorker/Workers.hs	Switches worker pools to transactionalWorkerConfig, removes dedicated Arbiter conn-str usage, and uses pool shutdown helpers.
services/background-worker/src/Wire/BackgroundWorker/Env.hs	Builds Arbiter migration connection string via mkArbiterConnectionString.
nix/haskell-pins.nix	Adds arbiter-worker-testkit pin entry.
libs/wire-subsystems/wire-subsystems.cabal	Adds postgresql-connection-string dependency to support new conn-str builder.
libs/wire-subsystems/src/Wire/JobSubsystem/Migrations.hs	Introduces mkArbiterConnectionString and clarifies migration-lock connection lifecycle.
libs/wire-subsystems/src/Wire/JobSubsystem/Interpreter.hs	Updates Arbiter API usage for inserting jobs and query execution.
libs/wire-subsystems/src/Wire/JobSubsystem/ArbiterAdapter.hs	Adapts to newer Arbiter MonadArbiter API (Query wrapper, placeholder numbering) and disables listener usage.
libs/wire-subsystems/default.nix	Adds postgresql-connection-string to Nix derivation inputs.
libs/wire-api/wire-api.cabal	Adds arbiter-core dependency for updated registry typing.
libs/wire-api/src/Wire/API/Jobs.hs	Updates JobRegistry to use Queue type from arbiter-core.
libs/wire-api/default.nix	Adds arbiter-core to Nix derivation inputs.
libs/extended/src/Hasql/Pool/Extended.hs	Removes the old connection-string helper (now provided by wire-subsystems).
flake.nix	Bumps Arbiter source revision.
flake.lock	Updates Arbiter lock metadata to match new revision.
docs/src/developer/reference/config-options.md	Updates operator docs to reflect shared-pool concurrency and removal of LISTEN/NOTIFY connection.
changelog.d/0-release-notes/WPB-26489	Updates release notes to match new connection/pool behavior and migration-lock connection lifecycle.

[blackheaven]

Why did you have to upgrade?

[battermann]

Why did you have to upgrade?

Then new version offers better use of postgres connections, keeping configuration tuning and overhead for operators to a minimum.