Make blog post on learning.mozilla.org/gigabit dynamic

[hannahkane]

New gigabit-tagged posts are added to https://learning.mozilla.org/blog/ monthly. Ideally, the most recent post tagged with "gigabit" would appear automatically on the "blog" section within the "Featured Updates" section of learning.mozilla.org/gigabit (similar to how blog posts are dynamically pulled into the Learning site homepage).

@Pomax @mmmavis @gvn - can one of you please advise and estimate the effort involved in this?

cc @jenntbeard