cdp-instances, a repo to simply store the config details for active instances

## Idea / Feature

A single repo that stores the configs and details for instances.

## Use Case / User Story

This is valuable to publish in both Python and JavaScript.
In JavaScript, it would make it easier to manage the `/instances` route on the `councildataproject.org` page. I.e. having all of the active instances in a single repo that is simply pulled into to other frontend libraries for quick access.

Same for Python. with https://github.com/councildataproject/cdp-data / CouncilDataProject/cdp-roadmap#3 it would be valuable to have a repo that we can pull in that has all the configs for the various instances.

## Other Notes

It might make sense like CouncilDataProject/cdp-backend#167 to use some sort of code generation to handle this.