Document: feat(iceberg): support iceberg jdbc catalog views

This issue tracks the documentation update needed for the merged PR #21400.

Source PR URL: https://github.com/risingwavelabs/risingwave/pull/21400
Source PR Merged At: 2025-04-17T06:19:11Z

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.