Export a models property in @inngest/ai (#890)

## Summary
<!-- Succinctly describe your change, providing context, what you've
changed, and why. -->

Export a `models` property in `@inngest/ai`, allowing us to easily grab
all supported models.

## Checklist
<!-- Tick these items off as you progress. -->
<!-- If an item isn't applicable, ideally please strikeout the item by
wrapping it in "~~"" and suffix it with "N/A My reason for skipping
this." -->
<!-- e.g. "- [ ] ~~Added tests~~ N/A Only touches docs" -->

- [ ] ~Added a [docs PR](https://github.com/inngest/website) that
references this PR~ N/A
- [ ] ~Added unit/integration tests~ N/A
- [x] Added changesets if applicable

## Related

- For #889

Author: jpwilliams

.changeset/unlucky-points-exercise.md

@@ -0,0 +1,5 @@
+---
+"@inngest/ai": patch
+---
+
+Export a `models` property containing all models

packages/ai/src/index.ts

@@ -1,3 +1,4 @@
 export type { AiAdapter, AiAdapters } from "./adapter.js";
 export * from "./adapters/index.js";
 export * from "./models/index.js";
+export * as models from "./models/index.js";