Give records a reference to the model manager which loaded them

[airhorns]

We have a few upcoming things that require records to be able to do stuff to themselves -- reload, select new fields from the backend, maybe record.save or similar, and I suspect more in the future. I still think they should act mostly as DTOs that don't have a lot of business logic on them, but if we want to be able to even know what model they are for, we need a reference to the thing that produced them! This passes along the model manager which instantiated a record to the record in both imperative API land and in React land.

In order to make this change work in React land, we need a new little bit of metadata exported from the generated client. Our React hooks get passed functions from the api client like useAction(api.post.create), so we need to be able to hop back from the create function that we get by reference to the api.post object. The generated client will need to decorate the create function with a reference, which is not super hard, but means that we have a backwards compatibility issue. @gadgetinc/react can't assume that it is upgraded at the same time as the api client, so it can't assume it is working against a newly generated api client that has this metadata.

For this reason, the model manager property on GadgetRecord is optional, which reflects the way it will be used in the real world without necessarily having that metadata available. When we go to build things like record.reload(), we can make that fail at runtime with a message saying "regenerate your client to get this to work!", instead of just assuming it is present.

Gadget side PR that tries this out: https://github.com/gadget-inc/gadget/pull/7201

[airhorns]

/cc @jasong689 I havent finished this but this was my thinking for the first step of how to build the someGadgetRecord.load("unloadedField") thing