Draft student progress API

[merkushin]

Here we have interfaces for entities: that's for simplicity. I think we don't need interfaces for them. However, I want to keep interfaces for repositories. The rough idea is that we implement repositories for storing in tables and in comments. And one "aggregating" implementation that keeps references to both implementations and decides which to use (by proxying calls) depending on conditions (feature flag or something else).

Changes proposed in this Pull Request

Testing instructions

New/Updated Hooks

Deprecated Code

Screenshot / Video