Read front-matter to configure the build

[alexeagle]

Rather than having to write a bunch of build rules to describe information about each file and its references, it would be neat to leverage some front-matter in yaml_library rules.

Notes:

• We could generate BUILD files using Gazelle, the current standard. I can contribute the extension (written in Starlark, not Go)
• Starting in Bazel 9, there is also a sneaky way to construct a dependency graph during execution phase by reading the yaml files to construct the yaml_library dependency tree
• A yaml_library rule also gives a better way to hookup yamllint with rules_lint

[jacobshirley]

That sounds great. It is currently a bit of a pain to have to specify each docs dependency. I will look into that Bazel 9 feature too, that sounds awesome