Update prod template with new aggregation host

[zwolf]

The internal kubernetes aggregation service name was changed from aggregation-caesar to aggregation-production-app to reflect the existence of the staging deploy and multiple services that make up the full deployment. This PR updates the env var that points to that service.

Review checklist

• First, the most important one: is this PR small enough that you can actually review it? Feel free to just reject a branch if the changes are hard to review due to the length of the diff.
• If there are any migrations, will they the previous version of the app work correctly after they've been run (e.g. the don't remove columns still known about by ActiveRecord).
• If anything changed with regards to the public API, are those changes also documented in the apiary.apib file?
• Are all the changes covered by tests? Think about any possible edge cases that might be left untested.