What does this mr do?

This MR improves the performance of counting the number of requests currently open for a certain lab for a certain assistant. It improves this by changing the current in-memory filter on requests by doing a specific query counting a filtered list of requests.

before

Lab.getQueuedCount counted the number of requests in a list of requests that fulfilled some conditions.

after

RequestRepository.queuedCountPredicate creates a predicate containing the checks previously in Lab.getQueuedCount.

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made.
• Tests were created to test the feature.
• I have updated the documentation accordingly.
• I adhere to the style guide.

Closes #93 (closed)