Refs #6846
This provides a way for pagination classes to add pagination properties (`count`, `next`, `results` etc.) to OpenAPI response schemas.
A new method `get_paginated_response_schema()` has been added to `BasePagination`. This method is intended to mirror `get_paginated_response()` (which takes a `list` and wraps it in a `dict`).
Hence, `get_paginated_response_schema()` takes an unpaginated response schema (of type `array`) and wraps that with a schema object of type `object` containing the relevant properties that the pagination class adds to responses.
The default implementation of `BasePagination.get_paginated_response_schema()` simply passes the schema through unmodified, for backwards compatibility.
This is the first part of #6846.
Previously, the response schema for list views was an object representing a single item. However, list views return a list of items, and hence it should be an array.
Further work will need to be done to support how pagination classes modify list responses.
There should be no change for views not determined to be list views.
