feat(webhooks): coordinate dispatch capacity with Redis (NAN-6407)

[agusayerza]

Summary

• coordinate SQS polling across autoscaled jobs instances with Redis-backed expiring permits
• adapt the shared concurrency limit from healthy admission latency and explicit overload feedback
• acquire capacity before receiving SQS messages and renew leases through acknowledgement
• add NANGO_TASK_DISPATCH_REDIS_COORDINATION_ENABLED as a rollout killswitch that preserves current per-instance polling when disabled

Stack

• stacked on feat(orchestrator): add webhook admission control (NAN-6404) #6870

Linear: NAN-6407

[linear-code]

NAN-6407

[cubic-dev-ai]

All reported issues were addressed across 9 files

Confidence score: 5/5

• Safe to merge after the addressed issues were fixed.

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 10 files

Confidence score: 5/5

• Safe to merge after the addressed issues were fixed.

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 5 files (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 4 files (changes from recent commits).

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 2 files (changes from recent commits).

<sub>Tip: Review your code locally with the cubic CLI to iterate faster.

Re-trigger cubic</sub>