feat: generate types for joins (#9054)

### What?
Generates types for `joins` property.
Example from our `joins` test, keys are type-safe:
<img width="708" alt="image"
src="https://github.com/user-attachments/assets/f1fbbb9d-7c39-49a2-8aa2-a4793ae4ad7e">

Output in `payload-types.ts`:
```ts
 collectionsJoins: {
    categories: {
      relatedPosts: 'posts';
      hasManyPosts: 'posts';
      hasManyPostsLocalized: 'posts';
      'group.relatedPosts': 'posts';
      'group.camelCasePosts': 'posts';
      filtered: 'posts';
      singulars: 'singular';
    };
  };
```
Additionally, we include type information about on which collection the
join is, it will help when we have types generation for `where` and
`sort`.

### Why?
It provides a better DX as you don't need to memoize your keys.

### How?
Modifies `configToJSONSchema` to generate the json schema for
`collectionsJoins`, uses that type within `JoinQuery`

test/select/payload-types.ts

@@ -21,6 +21,7 @@ export interface Config {
     'payload-preferences': PayloadPreference;
     'payload-migrations': PayloadMigration;
   };
+  collectionsJoins: {};
   collectionsSelect: {
     posts: PostsSelect<false> | PostsSelect<true>;
     'localized-posts': LocalizedPostsSelect<false> | LocalizedPostsSelect<true>;