Run statistics endpoint should take resolutions into account

[Etsija]

issuesCount, ruleViolationsCount and vulnerabilitesCount of the statistics endpoint do not yet take resolutions into account, which prevents using the counts in the run overview table.

[mnonnenmacher]

@eclipse-apoapsis/backend-devs I have discussed the implementation details for this issue with @Etsija and the solution will introduce some new tables that store the association of issues, rule violations, and vulnerabilities with their resolutions. This is required to guarantee that the statistics endpoint is performant, especially when showing statistics for whole products or organizations. These tables will also allow to make the implementation of other endpoints that need resolutions simpler and much more performant later on.
What we would not implement is filling those tables for old ORT runs, so the statistics would only work for new runs. The reason is that implementing this as a database migration would be very complicated and the migration would likely take a lot of time when many old runs need to be processed. We also discussed implementing this as a (task)[https://github.com/eclipse-apoapsis/ort-server/tree/main/tasks] but discarded the idea because there is currently no got setup for one-time tasks that can also store progress information.
Overall, the conclusion was that re-calculating the statistics for old runs is not worth the effort, especially as the problem will disappear over time when old runs get deleted. Please let us know when you disagree with that conclusion.