domain: add Identity & Access entities (User, Role, Permission, Group)

crates/domain/src/entities/mod.rs

@@ -1,2 +1,9 @@
+pub mod permission;
+pub mod role;
 mod user;
+mod group;
+
+pub use permission::{Permission, PermissionAction, ResourceType};
+pub use role::Role;
 pub use user::User;
+pub use group::Group;