Limit outstanding OPA requests

[EDsCODE]

Description

Large metadata scans can overwhelm the OPA HTTP destination queue because column filtering submits one request per table without a global bound.

This change limits outstanding OPA requests across all queries before submission. Permits return when each raw HTTP response future completes.

+ opa.max-outstanding-requests=512

The OPA plugin test suite covers the global concurrency limit, configuration mapping, formatting, dependencies, and style checks.

Additional context and related issues

• Related upstream issue: Open Policy Agent: Max requests queued per destination 1024 exceeded for HttpDestination trinodb/trino#25628
• Full reactor validation stopped when parallel modules could not resolve local snapshot artifacts.
• No open PostHog/trino pull request duplicates this change.
• CodeRabbit could not start its authentication callback, so this PR opened without a local pass.

Release notes

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## Security
* Prevent OPA access control metadata filtering from exhausting HTTP request queues.