Tag guides as "new" or "updated"

Related to https://github.com/bump-sh/docs/pull/215. I don't know what the limitations would be, but it would be great to have a view of "what's new" in the guides and potentially "what's been updated lately."

We're starting to have a decent amount of guides, and for our returning readers, it would be great to know quickly what is the freshest content by:
* seeing a "New" tag for a guide that has been initially published in the last 4 weeks
* (if possible, although less important) seeing an "Updated" tag for a guide which has been updated in the last 4 weeks. Worst case scenario, we can fallback on updating the prefix in the filename only for major updates of guides, and consider them as "New".
* having a list view of all "New" guides

Start by reviewing related pull request #215 and the existing guide organization in this repository. Determine how publication and update dates are represented, then define how guides receive “New” or “Updated” tags and how a list of new guides is presented. Done means the requested labels and list view work for the stated four-week window.

Written by the indexing model from the issue text.