Update dkan_search_api to automatically 'Rebuild tracking information' when new data is added

[janette]

How to reproduce

1. add dummy content and index the site
2. confirm that admin/config/search/search-api/index/dkanshows 10/10 indexed.
3. add a new dataset
4. go to admin/config/search/search-api/index/dkan
5. notice that it still says 10/10 indexed rather than 10/11

Acceptance Criteria

• [ ] Adding a new dataset automatically rebuilds tracking information
• [ ] Add a test to confirm