Additional annotated example recipes

### What problem does your feature request solve?

Currently there is a single annotated example recipe in the documentation. While this shows the basics, it doesn't show anything perticularily advanced, and is also only a single data point.

### Describe the solution you'd like

It would be good to have a selection of many different recipes of differing complexity, showcasing many different features. This is analogous to [matplotlib's plotting gallery](https://matplotlib.org/stable/gallery/). These examples should be heavily annotated so people can learn from them, and adapt them to their own needs.

### Describe alternatives you've considered

Should these recipes be just in the documentation, or be full recipes in CSET as well? It would be nice, as then we can ensure they always remain working (acting as additional tests), and we could include the output alongside the examples.

The issue names no files, tests, or entry points, so begin by locating the existing annotated example recipe and documentation structure. Done would mean adding a selection of heavily annotated recipes with differing complexity, with a decision on whether they should also be full CSET recipes that run as tests.

Written by the indexing model from the issue text.