Admin Tab for MAPLE News Items

[Mephistic]

Summary
For the upcoming "MAPLE in the News" page, we want Admin users to be able to add News articles/links to the page without requiring a code change/deploy. To that end, we should add a tab to the admin page (located at /admin) that allows Admin users to add News Items.

This will likely necessitate a new Firestore collection for newsItems, and a news item should have at least the following fields:

• url (Link to the article)
• type (One of article, award, or book - most items will be articles to start and other types may be added in the future)
• author (e.g. Medium / MSNBC / Harvard Kennedy School / etc.)
• title (Title of the article/book)
• description (The first X words/lines of the article)
• publishDate (Publish date of the article/book)
• createdAt (When our admin user created the News Item)

For now, we can safely assume there will be a relatively small number of news items (< 50), so pagination/filtering can wait until they become necessary.

This should be able to take advantage of the react-admin library that the Moderation tab uses.

[Mephistic]

This is the Admin component of #2045

To see how this will look on the Front End, the Figma for that issue is: https://www.figma.com/design/HCaEcZDGGXjhvvhOxKvUu3/Media--Articles---Insights?node-id=0-1&p=f&t=SiJ2feDoA4zoRxHn-0