RDSC-4603 Update RDI public documentation

[stoyanr]

See https://redislabs.atlassian.net/browse/RDSC-4603 and https://github.com/RedisLabs/redis-data-integration/pull/2565

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Note

Low Risk
Low risk: documentation-only changes, though broad updates could cause user confusion if any details or links are incorrect.

Overview
Adds extensive public docs for the new Flink stream processor alongside the existing classic processor, including a new architecture comparison page and a step-by-step migration guide.

Updates pipeline configuration and reference docs to expose processors.type (classic/flink), clarify which settings are classic-only vs. Flink-only (including processors.advanced), and document Flink-only features like expression/lookup caching and redis.lookup batching.

Refreshes install/upgrade/FAQ/observability guidance to cover Flink-specific images, Helm-level sizing knobs, and the new metrics model (Flink JobManager/TaskManager metrics vs. rdi-metrics-exporter), plus small clarifications and formatting cleanups across examples.

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[andy-stark-redis]

A couple of minor suggestions but otherwise LGTM.

[ZdravkoDonev-redis]

Suggested change

	The Flink processor does not use `rdi-metrics-exporter`. It exposes
	The Flink processor does not use `rdi-metrics-exporter` component. It exposes

[stoyanr]

I changed the docs to talk about "rdi-metrics-exporter service" everywhere consistently. This particular reference here I dropped as it was not needed.

[andy-stark-redis]

Suggested change

	you switch back without further edits.
	you switch back without further edits. Likewise, the Flink processor silently ignores the settings that only apply under classic.

[stoyanr]

I proposed a slightly different sentence, hopefully still ok.