Add UserPermissions as common code, add linting and test deps

src/UserPermissions/UserPermissionsCommon.js

+/** **************************************************************
+ Copyright (C) 2023 Eclipse Foundation, Inc.
+
+ This program and the accompanying materials are made
+ available under the terms of the Eclipse Public License 2.0
+ which is available at https://www.eclipse.org/legal/epl-2.0/
+
+  Contributors:
+    Martin Lowe <martin.lowe@eclipse-foundation.org>
+
+ SPDX-License-Identifier: EPL-2.0
+******************************************************************/
+const { z } = require('zod');
+const SUPPORTED_PERMISSION_LEVELS = ['READ', 'TRIAGE', 'WRITE', 'MAINTAIN'];
+const USER_PERMISSIONS_SCHEMA = z.object({
+  overrides: z.array(
+    z.object({
+      name: z.string(),
+      permission: z.enum(SUPPORTED_PERMISSION_LEVELS),
+      expiry: z.coerce.date(),
+      target_projects: z.array(z.string()),
+    })
+  ),
+  excluded: z.array(z.string()),
+});
+
+function castJsonToOverrideFormat(jsonString) {
+  return USER_PERMISSIONS_SCHEMA.parse(JSON.parse(jsonString));
+}
+
+module.exports.USER_PERMISSIONS_SCHEMA = USER_PERMISSIONS_SCHEMA;
+module.exports.castJsonToOverrideFormat = castJsonToOverrideFormat;