feat: add assistant model

[whplh]

Some model relations are going to change for version 2.5.0 (-> this pr is a draft)

• The api supports listing assistants and includes fields for relational fields only when the request parameters includes them.
• The api supports updating an existing assistant
• The api supports deleting an assistant

See tests for request examples.

Refs: HKI-81

[whplh]

@Ariansdf I updated the api to support json api,
which is supported by laravel 13 out of the
box.
For filtering the recommended Query bulider lib
was added. ( E.g. filtering for category like: /api/assistants?filter[category]=general)

[whplh]

I discovered the resource hooks from the laraveljsonapi package and refactored the code. With them the CRUD operations can pass through the laravelapi package/framework and let it do its thing and react to changes before or afterward.