feat: add list of aliases to note entity

One of the aliases can be primary for each note, but all can be used to get information from the apis.

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/notes/primary.value-transformer.ts

@@ -0,0 +1,22 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { ValueTransformer } from 'typeorm';
+
+export class PrimaryValueTransformer implements ValueTransformer {
+  from(value: boolean | null): boolean {
+    if (value === null) {
+      return false;
+    }
+    return value;
+  }
+
+  to(value: boolean): boolean | null {
+    if (!value) {
+      return null;
+    }
+    return value;
+  }
+}