(core) Persist forks in home db

Summary:
Adds information about forks to the home db. This will be used
later by the UI to list forks of documents.

Test Plan: Browser and server tests.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3772

app/gen-server/migration/1673051005072-Forks.ts

@@ -0,0 +1,42 @@
+import {MigrationInterface, QueryRunner, TableColumn, TableForeignKey} from "typeorm";
+
+export class Forks1673051005072 implements MigrationInterface {
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.addColumns("docs", [
+      new TableColumn({
+        name: "created_by",
+        type: "integer",
+        isNullable: true,
+      }),
+      new TableColumn({
+        name: "trunk_id",
+        type: "text",
+        isNullable: true,
+      }),
+      new TableColumn({
+        name: "type",
+        type: "text",
+        isNullable: true,
+      }),
+    ]);
+
+    await queryRunner.createForeignKeys("docs", [
+      new TableForeignKey({
+        columnNames: ["created_by"],
+        referencedTableName: "users",
+        referencedColumnNames: ["id"],
+        onDelete: "CASCADE",
+      }),
+      new TableForeignKey({
+        columnNames: ["trunk_id"],
+        referencedTableName: "docs",
+        referencedColumnNames: ["id"],
+        onDelete: "CASCADE",
+      }),
+    ]);
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.dropColumns("docs", ["created_by", "trunk_id", "type"]);
+  }
+}