Spike: investigate dynamic content for homepage filter chips

Created by: lguychard

Currently filter chips only show static, predefined content.

We want to show data that actually exists on the instance (repo names, file names, authors).

Strawman idea from @lguychard: if we run type:diff count:1 that will give us a valid repo name, file name, author, commit message. We could cache the results in temporary settings to avoid running this on every homepage load.

/cc @benvenker @lguychard