API counts for paginated routes

[youri-k]

Steps to test:

• make an api request to a paginated route
• look for X-Total-Count in response to show how many entries were found

Issues:

• fixes next to paginated API requests: provide counts #3666

---

• Updated changelog
• Updated documentation if applicable
• Ready for review

[fm3]

Thanks for this PR! This works well :-) However, I have a couple of thoughts:

• Performance: while counting the entries in the database uses way less resources than actually fetching them, it is still fairly slow for large collections. This is why I’d suggest to modify the routes to include an optional includeTotalCount boolean parameter defaulting to false. Only when this is set to true, run the count queries
• maintainability: I noticed some code duplication between the methods that fetch and the methods that count the records. Maybe some of their parts could be extracted to reusable methods (e.g. stateQuery for the annotation list)