docs: add changelog for 12576

changes/ce/breaking-12576.en.md

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+Starting from 5.6, the "Configuration Manual" document will no longer include the `bridges` config root.
+
+A `bridge` is now either `action` + `connector` for egress data integration, or `source` + `connector` for ingress data integration.
+Please note that the `bridges` config (in `cluster.hocon`) and the REST API path `api/v5/bridges` still works, but considered deprecated.