List collections of models

Example cURL request: ```console curl -s \ -H "Authorization: Bearer $REPLICATE_API_TOKEN" \ https://api.replicate.com/v1/collections ``` The response will be a paginated JSON list of collection objects: ```json { "next": "null", "previous": null, "results": [ { "name": "Super resolution", "slug": "super-resolution", "description": "Upscaling models that create high-quality images from low-quality images." } ] } ```