[changelog] Categories should be identifiable separatedly from their formatting

[aalmiray]

Categories have a title property that's used to render them on the changelog, as well as matching and merging settings applied by presets. This poses a problem when the formatting includes special character such as spaces and emojis.

I'd be better if categories had a key (identifier) used for matching and keep the title for rendering. For backward compatibility the value of key will be set to title if key is not explicitly defined.

CC @michael-simons @kcpeppe

[aalmiray]

@michael-simons @kcpeppe please use the key property on a category to match customizations made to the changelog.

[michael-simons]

Thanks @aalmiray for the heads up, works nicely:

michael-simons/neo4j-migrations@ffddee7