Taylor diagrams for inter-model comparisons

[Taylor diagrams](https://en.wikipedia.org/wiki/Taylor_diagram) are a useful way of comparing at a glance multiple different statistics between models.

The issue names no files, tests, or entry points. Start by locating the existing model-comparison and plotting workflows, then define which statistics, inputs, and output format the Taylor diagrams must support; done means a documented, tested comparison workflow produces the diagrams.

Written by the indexing model from the issue text.