refactor: move domains to package core/{domain}

[mabdh]

This is the first PR of some multiple tasks from this issue #121

Ideas
The structure would be layered like this

• [server(handler)/hook/middleware] > service > repository
• All components server(handler)/hook/middleware should talk to service layer to process data

Changes

• move all entities in model to its own domain
• move schema store interface to its own domain
• moving the definition vars to its domain package
• move authz spicedb to store layer
• move config to its domain SpiceDBConfig to spicedb.Config
• refactor the cyclic import
  • avoid import cycle user<>group move ListUserGroups in user domain/service to group domain/service, let user be an entity that does not depend on anything
• permission package has responsibility to all domains, need to separate to its own domain
  • relation package create function, pass a relation struct directly to store layer without picking the component to make the create function reusable
  • move relation functions to to the domain that uses it
• Refactor CheckPermission to CheckPermission(ctx context.Context, usr user.User, resourceNS namespace.Namespace, resourceIdxa string, action action.Action) (bool, error) to avoid having dependency to resource package.
• Move CheckAuthz function in permission to ResourceService
• remove structs package
• refactor some errors with prefix Err
• Move integration test to test/integration folder
• Rename v1.go to v1beta1.go

[mabdh]

converting this to draft as we need to test this manually first

[mabdh]

This PR will also solve #125