Support If-Modified-Since header in the API
Problem to solve
The If-Modified-Since header makes it easy for an API consumer to avoid transferring unnecessary data, and should save the server some work too.
From working with other RESTful APIs I'm surprised this option isn't availble.
Proposal
Add support for If-Modified-Since header for issues, merge requests, epic etc etc.
Many of these entities already include updated-at in the response so the server should be able to use this already.