chore: add option in librarian for license headers in grafeas (#13510)

Adds alternate headers for grafeas. Will wait to regenerate until
googleapis/librarian#6481 is merged.
For googleapis/librarian#6178

Author: sofisl

java-grafeas/license-header.txt

@@ -0,0 +1,15 @@
+/*
+ * Copyright 2026 The Grafeas Authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */

librarian.yaml

@@ -1856,6 +1856,7 @@ libraries:
       name_pretty_override: Grafeas
       product_documentation_override: https://grafeas.io
       skip_pom_updates: true
+      alternate_headers: license-header.txt
   - name: gsuite-addons
     version: 2.94.0-SNAPSHOT
     apis: