add CI for deleted/moved pages

[mrjones-plip]

Right now when doing a large (or even small!) reorganization of content, it's hard to track that every page has been redirected to it's new home. While hugo does a great job of checking that existing links within docs work, it has no way of knowing about nonexistant links from documents that were moved or deleted.

we should add a CI test that addresses this:

• written in node
• able to run both locally and in CI
• takes a snapshot of all production URLs and runs them against a branch
• reports all 404s and redirects

There's an existing set of URL map creating and URL map checking scripts that could be used as a functional model of what we're going for.

this work will not only benefit Medic teammates but the larger community for when changes are made.

cc @esthermmoturi