feat: add new user settings backend

Adding a new user settings backend and PersistentStorage to store user related settings in the
database.

Signed-off-by: Dominik Schwank <dominik.schwank@sda.se>

plugins/user-settings-backend/migrations/20220824183000_init.js

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * 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
+ *
+ *     http://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.
+ */
+
+/**
+ * @param {import('knex').Knex} knex
+ */
+exports.up = async function up(knex) {
+  await knex.schema.createTable('user_settings', table => {
+    table.comment('The table of user related settings');
+
+    table
+      .text('user_entity_ref')
+      .notNullable()
+      .comment('The entityRef of the user');
+    table.text('bucket').notNullable().comment('Name of the bucket');
+    table.text('key').notNullable().comment('Key of a bucket value');
+    table.text('value').notNullable().comment('The value');
+
+    table.primary(['user_entity_ref', 'bucket', 'key']);
+  });
+};
+
+/**
+ * @param {import('knex').Knex} knex
+ */
+exports.down = async function down(knex) {
+  await knex.schema.dropTable('user_settings');
+};