Unify default value handling for JSON-Schema generator

We started using victools-jsonschema-generator and have a custom default value handler.
It's currently also pulling in jakarta.ws.rs annotations, which we might not want to require.

This is a follow-on task.

Original comment:
I mostly added because it felt weird having jakarta annotations for validations (to include in the json schema), such as `@Positive`, as their standalone annotations, but the default value for a property was buried somewhere in the `@JsonProperty` annotation. I don't feel strongly about keeping this, though, it's just a handful of places which can be covered with the jackson annotation property.

_Originally posted by @kroepke in https://github.com/Graylog2/graylog2-server/pull/23462#discussion_r2429831533_