Feature request: Draftail Strikethrough

[keeganland]

Our editors would like to be able to do strikethroughs in the Rich Text editors in Wagtail.

Wagtail implements its Rich Text editor using Draftail. Plugins etc. can be added to Draftail, which is itself based on Draft.JS. The following documentation exists for writing or installing extensions to Draftail:

https://docs.wagtail.org/en/stable/extending/extending_draftail.html

Mention of enabling Draftail strikethrough on this page:

https://www.draftail.org/docs/formatting-options

It seems it should not be difficult to flip a few switches to get it enabled, we just need to read this documentation to see explicitly which ones