Sankey Charts and Funnel Charts

### What problem are you trying to solve?

It would be helpful to have Sankey and Funnel charts in dbt-charts.

Both of them are useful for visualizing flows of entities through processes although in differing ways.

I'd like to use the Sankey chart to visualize flows of money into and out of a company. Like this: https://www.sankeyart.com/

A funnel chart is good for answering the question "how many of X made it all the way through a selection process." I have a use case where I have a bunch of PDFs, with new PDFs coming in every day, which move through a multi-step data extraction process. PDF -> free text -> structured JSON -> LLM-summarized meaning. A funnel is a great way to visualize this. Another example of a useful funnel chart: https://www.atlassian.com/data/charts/funnel-chart-complete-guide

### Proposed YAML syntax

I think it's just a new entry under "type" for "sankey" and "funnel"

### Why can't an existing field cover this?

Not a new field per se, instead new values accepted and processed in an existing field. Although I'm not sure of what the field configuration details would at lower levels below "type".