Format YAML Front Matter in vertical 2 column table

[morallo]

Currently, the only way that a YAML Front Matter data section is rendered is in a single-row table with 1 column per field. This does not scale when there are many variables.

It would be very nice to be able to flag the Front Matter with a specific variable that tells GitHub how to render it. Something like:

yaml-frontmatter-layout: vertical

Or you may combine it with my proposed solution for #994:

yaml-frontmatter-display: vertical