Document: fix(frontend): cursor should not be schema-bound

This issue tracks the documentation update needed for the merged PR #20221.

Source PR URL: https://github.com/risingwavelabs/risingwave/pull/20221
Source PR Merged At: 2025-01-22T11:07:40Z

If it is a major improvement that deserves a new page or a new section in the documentation, please check if we should label it as an experiment feature.