feat: allow group fields to have an optional name (#12318)

Adds the ability to completely omit `name` from group fields now so that
they're entirely presentational.

New config:
```ts
import type { CollectionConfig } from 'payload'

export const ExampleCollection: CollectionConfig = {
  slug: 'posts',
  fields: [
    {
      label: 'Page header',
      type: 'group', // required
      fields: [
        {
          name: 'title',
          type: 'text',
          required: true,
        },
      ],
    },
  ],
}
```

will create
<img width="332" alt="image"
src="https://github.com/user-attachments/assets/10b4315e-92d6-439e-82dd-7c815a844035"
/>


but the data response will still be

```
{
    "createdAt": "2025-05-05T13:42:20.326Z",
    "updatedAt": "2025-05-05T13:42:20.326Z",
    "title": "example post",
    "id": "6818c03ce92b7f92be1540f0"

}
```

Checklist:
- [x] Added int tests
- [x] Modify mongo, drizzle and graphql packages
- [x] Add type tests
- [x] Add e2e tests

test/types/payload-types.ts

@@ -144,6 +144,10 @@ export interface Post {
   text?: string | null;
   title?: string | null;
   selectField: MySelectOptions;
+  insideUnnamedGroup?: string | null;
+  namedGroup?: {
+    insideNamedGroup?: string | null;
+  };
   radioField: MyRadioOptions;
   updatedAt: string;
   createdAt: string;
@@ -264,6 +268,12 @@ export interface PostsSelect<T extends boolean = true> {
   text?: T;
   title?: T;
   selectField?: T;
+  insideUnnamedGroup?: T;
+  namedGroup?:
+    | T
+    | {
+        insideNamedGroup?: T;
+      };
   radioField?: T;
   updatedAt?: T;
   createdAt?: T;