RDSC-5610: Multi-source documentation

[andy-stark-redis]

Recreated from #3916 after its base branch (RDSC-6038-rdi-2.0.0-release-notes) was deleted following #3996's squash-merge, which auto-closed the original PR and left it unable to be reopened via the API (GitHub disallows retargeting a closed PR's base). Same head commit, same diff — see #3916 for the original review history.

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See https://redislabs.atlassian.net/browse/RDSC-5610

Enhances #3841 with numerous changes and additions. I couldn't update the original PR since I don't have write permissions to this repository.

Note that it now documents 2 PRs that are not yet merged, but should be before the release:

• https://github.com/RedisLabs/redis-data-integration/pull/2782
• https://github.com/RedisLabs/redis-data-integration/pull/2791

Release-note additions

The release notes add the Collector API startup fix for OpenShift, identifying it as a regression introduced in RDI 1.19.1. The Flink processor and collector security entry adds 15 CVE identifiers from the final 2.0.0 changelog, preserving all existing identifiers.

Validation for this update: confirmed that the diff contains only these two changes, checked the security identifiers against the 2.0.0 changelog, and ran git diff --check. The Hugo build was not rerun for this text-only update.

Generated documentation consolidation

The OpenAPI version is set to 2.0.0 in commit dcc84dbfb, taking the only new API/schema content from generated PR #4026. The full parsed OpenAPI document now matches #4026. The configuration references are equivalent apart from formatting, and the reviewed API migration and CLI documentation in this PR is retained. #4026 is closed as superseded.

Validation: parsed JSON comparison with #4026, confirmation that only info.version changed in this commit, and git diff --check passed.

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Note

Low Risk
Documentation-only changes in the docs repo; no application code is modified, though readers must follow the new upgrade and secret guidance when moving to RDI 2.0.0.

Overview
Updates Redis Data Integration docs for RDI 2.0.0 (rdi_current_version in config.toml) and documents multi-source pipelines, per-database secrets, and several 2.0 breaking operational changes.

Multi-source: New guide Multiple sources in one pipeline covers naming rules, config.yaml with several sources, job server_name (and Flink list/regex matchers), per-source collectors/metrics/DLQ keys, and add/remove/start/stop/reset with --source. Architecture, pipelines, FAQ, and API migration now state that v2 is required for multiple sources and that legacy upgraded sources keep SOURCE_DB_*, server_name: rdi, and old stream names until removed or the pipeline is cleared.

Secrets & deploy: Secret management is rewritten around generic keys (USERNAME, PASSWORD, CACERT, …) plus redis-di set-secret --db <source|target>, derived env vars like ${MYSQL_DB_PASSWORD}, and K8s secrets named <source>-db / <source>-db-ssl. Prepare-database pages and examples are aligned to that model.

Processor & upgrade: Default stream processor is documented as Flink (explicit classic to opt out). Upgrade and classic→Flink migration guides add drain-before-switch steps, 2.0.0-specific warnings, and redis-di deploy --empty (and API v2 empty PUT) replacing pipeline delete/undeploy. Observability and HA examples use per-source collector names (e.g. collector-mysql). Minor image pin updates appear in the K8s install doc (Debezium, RIOT-X).

^{Reviewed by Cursor Bugbot for commit dcc84db. Bugbot is set up for automated code reviews on this repo. Configure here.}

[andy-stark-redis]

Superseded by #4029, which resolves the merge conflicts against main (this PR's branch lives on a fork I can't push a resolution to).