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"

enterprise/coderd/coderd_test.go

@@ -497,7 +497,7 @@ func testDBAuthzRole(ctx context.Context) context.Context {
 		ID: uuid.Nil.String(),
 		Roles: rbac.Roles([]rbac.Role{
 			{
-				Name:        "testing",
+				Identifier:  rbac.RoleIdentifier{Name: "testing"},
 				DisplayName: "Unit Tests",
 				Site: rbac.Permissions(map[string][]policy.Action{
 					rbac.ResourceWildcard.Type: {policy.WildcardSymbol},