chore: create type for unique role names (#13506)

* chore: create type for unique role names

Using `string` was confusing when something should be combined with
org context, and when not to. Naming this new name, "RoleIdentifier"

coderd/database/dbauthz/setup_test.go

@@ -123,7 +123,7 @@ func (s *MethodTestSuite) Subtest(testCaseF func(db database.Store, check *expec
 		az := dbauthz.New(db, rec, slog.Make(), coderdtest.AccessControlStorePointer())
 		actor := rbac.Subject{
 			ID:     testActorID.String(),
-			Roles:  rbac.RoleNames{rbac.RoleOwner()},
+			Roles:  rbac.RoleIdentifiers{rbac.RoleOwner()},
 			Groups: []string{},
 			Scope:  rbac.ScopeAll,
 		}