Migrate to the `cflinuxfs4` cloud.gov stack

[cantsin]

cflinuxfs3 support is ending (ref).

We need to update the cflinuxfs4 stack for all environments and test expected behavior:

• manifest-production.yml
• manifest-staging.yml
• tock/maintenance_page/manifest.yml

[edwintorres]

Is this one done? @cantsin

[cantsin]

Yep! 🎉