Update CodeOcean-related meta data automatically

[MrSerth]

For tasks imported from CodeOcean, we usually have some metadata stored. These contain general task-specific information (such as the execution environment) and some file-related information (e.g., the desired file role). For those file-related meta-data, we could consider updating them automatically.

Example Use Case: A file imported from CodeOcean with XML ID 1 has metadata stored as CO-1. Now, said file is removed from CodeHarbor. Consequentially, we could remove the metadata belonging to CO-1 as well.