Make purge crawl pagination lazy

### Problem Description

Pagination for the purge crawl feature isn't paginated, so all IDs are stored in memory during the sync. This could cause problems for users that need to purge very large amounts of docs.

### Proposed Solution

Make the pagination lazy so we can avoid this.

### Additional Context

Came up in this PR: https://github.com/elastic/crawler/pull/65#discussion_r1711771484