FEM Switcheroo: Phase One

[zwolf]

• Migrates fe-content-pages routes to fe-root. Locations /about and /get-involved now use prefix matches that point to fe-root.zooniverse.org. Included this change in both production and staging redirect configurations (with staging pointing to fe-root.preview).
• Removes the /about/(_next|assets)/ location block since that's covered by the prefix match.
• Adds the fe-root.zooniverse.org host to the zooniverse.org ingress. Requires Add fe-root resources to production k8s template front-end-monorepo#6273 to deploy first to create that service.

When this merges and deploys to staging, it will override the current, manually-tagged staging deploy. Changes in this PR can then be tested on static-staging.zooniverse.org which will once again be at parity with production, plus this PR. Subsequently deploying to production will complete Phase One of the Switcheroo in preparation for the Great Switch Pull next week.

edit: Requesting a handful of reviewers who might wanna take a look. If no one can get to it, I can smash the admin merge button.

[lcjohnso]

LGTM! I needed to get up-to-date re: the plan to switch all /about and /get-involved traffic in this phase (via this Slack thread between Zach and Delilah), but sounds good.