DOC: Add open source diagram tooling

Is your feature request related to a problem?

Some concepts in Xarray may be difficult to understand without visualizations, however vizualizations are currently hard to maintain and update (e.g., if its created using proprietary software, or if the file stored in the repo is the exported file instead of the original source file).

Having tooling to automatically build source outputs and use those outputs in the documentation would be really helpful.

Describe the solution you'd like

We can use https://kroki.io/ which allows us to create diagrams from a whole range of textual descriptions listed here https://kroki.io/#support

Pixi makes this sort of thing really easy (especially the https://prefix.dev/channels/github-releases channel, which pretty much makes any binary released on GitHub Pixi installable).

This issue is mostly lifted from https://github.com/Parcels-code/Parcels/issues/2532

Describe alternatives you've considered

No response

Additional context

Are diagrams something that we would benefit from? One example is https://github.com/pydata/xarray/issues/11031 , any others?

cc @ianhi

Review the Kroki support list and the Pixi GitHub Releases channel, then inspect the example in xarray issue 11031 and the source Parcels issue. Define which diagrams and documentation outputs should be supported; done means diagrams can be maintained from textual sources and automatically built into the documentation.