fix: assorted CSP issues

[thecristen]

Summary of changes

Asana Ticket: Add Soundcloud to CSP list so we can embed it and Map tiles should load on production environment

• After fix: change metro map config tile URL for prod #2322 the map tiles couldn't load as they were blocked by the CSP! So the first commit should fix that.
• The second commit adds a missing Google Tag Manager URL that I noticed logged in the console on mbta.com
• The third commit removes an old link from the root template that I only noticed because the CSP yelled about it 😅 The flatpickr library code is distributed with Metro now anyway.
• The fourth commit goes ahead and adds the Soundcloud URL.