Grouping of Releases

Due to the high number of releases, the selection fields for releases are currently very long. Therefore, we need a solution that enables more efficient management.
It would be beneficial to offer a grouping of releases to improve the overview and management. This grouping should apply to both existing and newly created releases.
The grouping could look similiar to the grouping functionality in the Quality Module. 1-2 levels of grouping would be already sufficient. 

Currently, there are several bugs when filtering by programs:
- Programs can only be selected in the backlog and not in release management.
- When filtering, only the releases that are actually assigned to a program should be displayed. Currently, releases that are not assigned to any program are also displayed.