Add human-readable citation summary

[garethrees]

A short summary of a citation could make users more interested in following the trail.

Similar to #6846, we could either allow this to be completely user-populated, pull it in dynamically on the form, or fetch it post-save in a background job. Most news sites will have some sort of <meta> tag containing a short summary of the content.

I don't think we'd render this on the request page since it would become messy, but it would be suitable to render on #6701.

Suggested in #5483 (comment).

[HelenWDTK]

This issue has been automatically closed due to a lack of discussion or resolution for over 12 months.
Should we decide to revisit this issue in the future, it can be reopened.