Enable state ECPS runs

[anth-volk]

Fixes #1986

This must be merged before merging the solution to PolicyEngine/policyengine-app#2216. This also requires a minor change to the production database, so once this is approved, please drop a message in this thread so that I can do so before merging the approved code.

This PR creates a new policy descriptor, "dataset", that the back end consumes and stores, in order to allow any given region to be run against an enhanced CPS sim run. At the moment, the only possible value of for this descriptor is "enhanced_cps". However, the PR maintains backward compatibility with the "enhanced_us" region that we previously used for US-wide enhanced CPS runs.

[anth-volk]

Going to also work #2015 into this PR

Note: If #2006 is merged before this, merge conflicts will need to be solved

[nikhilwoodruff]

Thanks! This looks great. But just thinking about backwards compatibility- do we need to add a general redirect on the app side for old links?

Edit: reading comprehension fail. Though does raise the question of whether the compatibility should be API side or app side.

[anth-volk]

You know, you make a good point - we could just use one redirect for inbound links. Let me think through this a bit. I might make some modifications and re-request review afterward. If that'd be cleaner and easier, I'm all for it, I just want to make sure it doesn't make loading time extreme for users.