feat: more role backend and admin/writer roles additions and adjustments

test/media_purge_qa_test.go

@@ -28,7 +28,7 @@ func TestPurgeRoleGuardIsAnAllowlist(t *testing.T) {
 
 				rec := env.send(t, route.method, route.path, "", 20)
 
-				expectRaw(t, rec, 403, apperr.OwnerOrAdminRequiredErrorMessage+"\n")
+				expectRaw(t, rec, 403, apperr.MissingPermissionErrorMessage+"\n")
 				if env.purgeSettings.getCalls != 0 || env.purgeSettings.saveCalls != 0 {
 					t.Errorf("expected no purge setting access")
 				}