Closes: https://github.com/fleetdm/fleet/issues/6493
Changes:
- Added a new action, `get-one-rss-feed.js`. This action generates and
returns RSS feeds for article categories on fleetdm.com.
- This action has one required input: `categoryName`.
- Lives at `/rss/[Article Category Name]` e.g.,
`fleetdm.com/rss/releases`
- If `articles` is provided as the category, it returns an RSS feed of
all articles published on our blog.
- Updated `view-basic-article.js` to set an `articleCategorySlug`
variable, that is used to link to the RSS feed for an article category
from an article page.
- Added a "subscribe" button to articles and article category pages that
links to an RSS feed for that category.
