Redesign "snapshots" to be "operations"

Right now, collaborating with multiple developers using the migration generator can be cumbersome. You have to remove any generated migrations locally, pull, and then regenerate migrations. This is because snapshots essentially are a linear process.

If we rearchitect this to use a single json file with an array of operations that have been generated, and then have the snapshots derived as a projection of those operations, then there will no longer be issues w/ multiple developers working together with the migration generator (e.g on different branches).