(core) add minimal support for activation keys

Summary: For grist-ee, expect an activation key in environment variable `GRIST_ACTIVATION` or in a file pointed to by `GRIST_ACTIVATION_FILE`. In absence of key, start a 30-day trial, during which a banner is shown. Once trial expires, installation goes into document-read-only mode.

Test Plan: added a test

Reviewers: dsagal

Reviewed By: dsagal

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3426

app/gen-server/migration/1652273656610-Activations.ts

@@ -0,0 +1,39 @@
+import {MigrationInterface, QueryRunner, Table} from 'typeorm';
+
+export class Activations1652273656610 implements MigrationInterface {
+
+  public async up(queryRunner: QueryRunner): Promise<any> {
+    // created_at and updated_at code is based on *-Initial.ts
+    const sqlite = queryRunner.connection.driver.options.type === 'sqlite';
+    const datetime = sqlite ? "datetime" : "timestamp with time zone";
+    const now = "now()";
+    await queryRunner.createTable(new Table({
+      name: 'activations',
+      columns: [
+        {
+          name: "id",
+          type: "varchar",
+          isPrimary: true,
+        },
+        {
+          name: "key",
+          type: "varchar",
+          isNullable: true,
+        },
+        {
+          name: "created_at",
+          type: datetime,
+          default: now
+        },
+        {
+          name: "updated_at",
+          type: datetime,
+          default: now
+        },
+      ]}));
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<any> {
+    await queryRunner.dropTable('activations');
+  }
+}