feat: Implement `UpdateGroup` Resolver

Created by: Tirokk

Pull Request

Implement UpdateGroup resolver.

Issues

• relates #5131 (closed)
• relates #5059 (closed)

Todo

• GraphQL
  • add group settings ( details see https://github.com/Ocelot-Social-Community/Ocelot-Social/issues/5059#user-content-group-settings )
    • categories
    • avatar
    • location
• tests:
  • general
  • slugification
    • if we change the name so that an existing slug will be generated that it is made unique by *-1
  • test if resolver Group finds group by id
  • does avatar testing make sense this way in backend/src/schema/resolvers/user_management.spec.js
    • minimum: await is missing …
    • search for other appearances of avatar: Factory.build('image', or Factory.build('image' without await
    • created an issue #5256 (closed)
• cleanup: search for Wolle