Add an extension type for incorporating _brand.yml

[jonpeake]

Description

As discussed in #12620, the best option to provide an easy way to add a _brand.yml file (and associated logo files) to an existing project/file would be an extension. However, the current options for creating an extension limit the utility of this. The closest approximation to creating an extension for this appears to be using the metadata format. However, the fact that this only adds metadata at the project level, while brand: is provided at the base level, means that there is still a separate manual step to add a line to _quarto.yml (or an individual file header) to incorporate the _brand.yml file into the rendered product. This, combined with the current bugs in how relative paths are treated for logos, leads to an overall inefficient (and in some cases, broken) workflow for adding a _brand.yml file to an existing quarto project/file.

Ideally, this would be fixed through a dedicated "brand" extension type for publishing a _brand.yml file and its associated files (i.e., adding a brand: option to contributes: . However, even allowing the "metadata" type to append to the root YAML level would fix this in the short term.

[cscheid]

Thanks for the comment! This is definitely a shortcoming. We'll have something like that to share with all of you sooner rather than later (we expect it by the time 1.8 is out)

[jonpeake]

Awesome, thank you for the quick response!