Support an "archived" tag on folders and documents

Problem Description

As systems and workflows are deprecated, it is often useful to keep around old documentation around. I propose adding a way to "archive" documents similar to Github's archive feature to denote documents that may no longer be up to date, but could still be worth keeping for reference.

Feature

• Adding a | archived tag to a document should put mark that page as archived. Adding an | archive tag to a folder will mark the folder as archived, as well as its home page and any nested folders and documents.
• Archived documents will show with an archived badge somewhere on the page.

Stretch goals

• Adjust search results to de-emphasize archived pages?