PROD-4233
Adds a new SearchAfterMixin to be added in place of PkSearchableMixin that allows using search_after. Once this mixin is used, it will bypass the default search limit of 10k by making multiple calls to ES in case we have more than 10k records in an index.

Previously, we faced an issue regarding the search limit, resulting in less records to be returned. We increased the MAX_RESULT_WINDOW before but a better way is to use search_after capability for an optimal and flexible result.

This PR also adds a v2 CatalogQueryContainsViewSet that fixes the querying mechanism by filtering the items at the time of when we're executing queries on ES. In v1, our CatalogQueryContainsViewSet first searched all the records AND THEN filtered it.

Testing Instructions:

1. Run update_index locally in Discovery shell.
2. Visit /api/v1/catalog/query_contains/ endpoint and add a sample query like this: http://localhost:18381/api/v2/catalog/query_contains/?course_uuids=2de67490-f748-4efd-8532-b445f7ecc6f9,f9f1e100-668a-4fd5-a966-a127de1f69de&query=org:edX

You can set ELASTICSEARCH_DSL_QUERYSET_PAGINATION to your specific value in order to test the behavior. While the end result will be the same but this can affect the number of times the search_after mechanism is called.