docs: Edge Proxy operational guide

[gagantrivedi]

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Changes

Contributes to #7207

Extends docs/docs/deployment-self-hosting/edge-proxy.md with operational guidance that the existing setup-and-config doc didn't cover, addressing the recurring support patterns catalogued in the issue:

• Identity overrides — explicit statement of behaviour, the Use identity overrides in local evaluation requirement, and the v2.21.1 deletion-propagation note.
• Troubleshooting — symptom-first guides for 401, 403 (with step-by-step diagnosis), restart loops in ECS/K8s, stale flags after dashboard changes, and incorrect identity-based evaluation.
• Production deployment — guidance for reverse proxy / load balancer setups, ECS/Fargate, Kubernetes (with a minimal Deployment manifest), and managing config.json as a secret in CI/CD.
• Architecture and scaling — stateless model, polling-load implications of horizontal scale, when endpoint caches help, and a reference RPS table from internal benchmarks.

The Rust Edge Proxy section called out in the issue is intentionally out of scope for this PR.

How did you test this code?

Docs-only change, no runtime behaviour to test

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Project	Deployment	Actions	Updated (UTC)
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[Holmus]

Really, really solid overall! most comments are nits about line breaks, eventually i stopped commenting on each one as it was just too many and i was not even sure whether they are mistakes or not.

Some real questions and comments but nearly there.

[Holmus]

Awesome, thanks for this!