feat(plugin-search): pass collection slug to beforeSync hook (payloadcms#11581)

The following is the use case.

```typescript
plugins: [
    searchPlugin({
      collections: ['products', 'posts'],
      beforeSync: ({ originalDoc, searchDoc,collectionSlug }) => {
        return {
          ...searchDoc,
          title: collectionSlug === 'products' ? originalDoc.name : originalDoc.title,
        }
      },
    }),
]
```

---------

Co-authored-by: Paul Popus <paul@payloadcms.com>

Author: 2 people

packages/plugin-search/src/types.ts

@@ -19,6 +19,7 @@ export type DocToSync = {
 }
 
 export type BeforeSync = (args: {
+  collectionSlug: string
   originalDoc: {
     [key: string]: any
   }

packages/plugin-search/src/utilities/syncDocAsSearchIndex.ts

@@ -79,6 +79,7 @@ export const syncDocAsSearchIndex = async ({
       })
     }
     dataToSave = await beforeSync({
+      collectionSlug: collection,
       originalDoc: docToSyncWith,
       payload,
       req,