Add ProductArea service

[jeffdaley]

Adds a ProductArea service to fetch and store product areas.

Currently these functions live in the ProductSelect component, so there's no caching, and state is reset on every render. This means we're fetching and loading more than we should. With a service, we can fetch the list once and it'll persist the session.

I'll soon use this service to add productArea to the /new model, which should improve that route's UX.

Observe the problem on main

• Create a RFC and watch for the ProductArea dropdown's loading state. (You can refresh if you miss it.)
• Click the back button
• Click the RFC tile again
• Notice the ProductArea dropdown's unnecessary loading state

[jfreda]

Nice - we discussed offline about perhaps exploring using Ember Data instead of a service per endpoint like this, but this seems like a good improvement to the current implementation 👍