[fix] [permissions] Fix role assignment at sign-up (#11045)

In [a previous PR](https://github.com/twentyhq/twenty/pull/11023) I
fixed the issue where users where re-assigned the default role when
signin up using SSO.
The "fix" actually introduced another error, calling
`assignRoleToUserWorkspace` only when a user is signing up to twenty,
forgetting about the case where an existing twenty user signs up to a
different workspace. They should still be assigned the role in that
case.

To fix this and improve clarity, I moved assignRoleToUserWorkspace to
addUserToWorkspace and renamed addUserToWorkspace to
addUserToWorkspaceIfUserNotInWorkspace since this is at each sign in but
does nothing if user is already in the workspace.

I think ideally we should refactor this part to improve readability and
understandability, maybe with different flows for each case: signIn and
signUp, to twenty or to a workspace

packages/twenty-server/src/engine/metadata-modules/permissions/utils/permission-graphql-api-exception-handler.util.ts

@@ -25,6 +25,7 @@ export const permissionGraphqlApiExceptionHandler = (
     case PermissionsExceptionCode.ROLE_NOT_FOUND:
     case PermissionsExceptionCode.USER_WORKSPACE_NOT_FOUND:
       throw new NotFoundError(error.message);
+    case PermissionsExceptionCode.DEFAULT_ROLE_NOT_FOUND:
     default:
       throw new InternalServerError(error.message);
   }