Restore `AUTOGENERATED_END` in time-window function docs

The `Docs autogenerate` nightly fails because the `windowID` removal deleted the closing generated-region marker together with the generated section. Restore the marker before the hand-written related-content section.

CI: https://github.com/ClickHouse/ClickHouse/actions/runs/33482157206/job/99777625358#step:4:808