Automatically generate displayName kewords in TOC files

[gewarren]

In the sprint meeting today, we discussed a tool that automatically pulls F1 keyword metadata from each linked article in a toc.yml file into the toc.yml file as displayName keywords (used in TOC filtering).

• If there are already displayName keywords, use the union of those and the F1 metadata, and select distinct items.
• If there are no F1 keywords in the linked article, skip that TOC entry.