Add variant support for checks

A field should be added to checks so that you can have a filter to import it or not. This filter should not be binary, but a list of tags, so that different types of reviews can be performed, either with different depths, focus areas or approaches.

A possibility would be adding the field `topics` as a list, which could contain values such as `design`, `implementation`, `alz`, etc.

Each checklist client would then decide whether importing all `topics`, or just a subset.

No files, tests, or entry points are named. Start by locating the check definitions and the checklist clients that import them, then trace how checks are selected. Done means checks can declare a list of topics and clients can select all topics or a subset without losing existing imports.

Written by the indexing model from the issue text.