docs/tutorial: load YAML data and validate it against some CUE using the Go API

[jpluscplusm]

We should have the example at https://cuelang.org/docs/concept/how-cue-works-with-go/#loading-non-cue-data as a stand alone, searchable-by-title page.

This example probably shouldn't be exposed as a howto, as the reader-use-case branching possibilities will quickly get very broad. Scoping this as a tutorial will allow the singular path through the example to be presented.

Use an existing tutorial as a template and example of the kind of instructions and language to use. https://cuelang.org/docs/tutorial/loading-cue-go-api/ is a good example.