docs(comparison): add a CARTO column

Adds CARTO as the fifth product column across the five comparison tables,
covering the existing 44 rows, plus a "Choose CARTO when" paragraph.

Values come from CARTO's public documentation and follow the page's convention
of describing mainstream out-of-the-box behavior. Rows with no documented
capability are marked "—" rather than filled speculatively.

Refs #1759

Author: srtena