I'm wondering how I could create some sort of chart/graph that shows me how many issues are in each status for every day, e.g. how many were in done on 15/05, 16/05, 17/05, 18/05, etc. and have this an ongoing thing for us to report on.
A cumulative flow diagram (CFD) displays what you note: the count of items in each status, day by day, as well as the cumulative count of done items.
Atlassian's interpretation of this chart is available for both Company-managed and Team-managed projects. To learn more please look at this documentation, depending upon your project type:
There are other/better versions of a CFD available from the Atlassian Marketplace from app vendors. Please investigate those if you find the Atlassian version does not match your needs: https://marketplace.atlassian.com/search?hosting=cloud&product=jira&query=cumulative%20flow%20diagram