Prep for more model providers

Adds a `modelProvider` field to `promptVariants`, currently just set to "openai/ChatCompletion" for all variants for now.

Adds a `modelProviders/` directory where we can define and store pluggable model providers. Currently just OpenAI. Not everything is pluggable yet -- notably the code to actually generate completions hasn't been migrated to this setup yet.

Does a lot of work to get the types working. Prompts are now defined with a function `definePrompt(modelProvider, config)` instead of `prompt = config`. Added a script to migrate old prompt definitions.

This is still partial work, but the diff is large enough that I want to get it in. I don't think anything is broken but I haven't tested thoroughly.

src/state/sync.tsx

@@ -0,0 +1,30 @@
+import { useEffect } from "react";
+import { api } from "~/utils/api";
+import { useExperiment } from "~/utils/hooks";
+import { useAppStore } from "./store";
+
+export function useSyncVariantEditor() {
+  const experiment = useExperiment();
+  const scenarios = api.scenarios.list.useQuery(
+    { experimentId: experiment.data?.id ?? "" },
+    { enabled: !!experiment.data?.id },
+  );
+  useEffect(() => {
+    if (scenarios.data) {
+      useAppStore.getState().sharedVariantEditor.setScenarios(scenarios.data);
+    }
+  }, [scenarios.data]);
+}
+
+export function SyncAppStore() {
+  const utils = api.useContext();
+
+  const setApi = useAppStore((state) => state.setApi);
+
+  useEffect(() => {
+    console.log("setting api", utils);
+    setApi(utils);
+  }, [utils, setApi]);
+
+  return null;
+}