R1:3e589cdd73ba

Add a workflow for populating (or depopulating) the common ngrams table

Summary:
Depends on D18672. Ref T13000. This does an on-demand build of the common ngrams table.

Plan here is:

- Push to `secure`.
- Build the common ngrams table here.
- See if stuff breaks?

If it looks okay on this dataset, we can build out the GC support and try it in production.

Test Plan:
- Locally, my dataset has a bunch of `bin/lipsum` tasks with similar, common words.
- Verified that ipsum terms now skip ngrams.