Improve filtering setup to make it easier to add new filtering fields

[dhruvkb]

Problem

The filtering setup is entirely located inside search.py disconnected from the media models. This poses an issue that changes to the models might allow these mappings to go out of sync when columns are modified.

Originally raised in this comment by @AetherUnbound on PR #699.

Description

The goal is to improve the filtering setup by colocating this list somewhere close to the models, so that changes to the models can keep this list valid.

Implementation

• [ ] 🙋 I would be interested in implementing this feature.