Add Heatmap chart type

[mediabakery]

A new HEATMAP chart type to Shaper.

The new chart renders date-based numeric data as a GitHub-style calendar heatmap, useful for visualizing activity, contributions, usage, events, or other daily counts over time.

Example

SELECT 'Activity'::LABEL;

SELECT
  date_trunc('day', created_at)::XAXIS,
  count(*)::HEATMAP
FROM events
GROUP BY ALL
ORDER BY ALL;

[mediabakery]

@jorinvo I’m not sure if this goes against the roadmap and is heading in completely the wrong direction. Please don’t hesitate to reject this merge. I don’t want to bloat the code unnecessarily. ;)