(core) Add Support Grist page and nudge

Summary:
Adds a new Support Grist page (accessible only in grist-core), containing
options to opt in to telemetry and sponsor Grist Labs on GitHub.

A nudge is also shown in the doc menu, which can be collapsed or permanently
dismissed.

Test Plan: Browser and server tests.

Reviewers: paulfitz, dsagal

Reviewed By: paulfitz

Subscribers: jarek, dsagal

Differential Revision: https://phab.getgrist.com/D3926

app/gen-server/migration/1682636695021-ActivationPrefs.ts

@@ -0,0 +1,16 @@
+import {nativeValues} from 'app/gen-server/lib/values';
+import {MigrationInterface, QueryRunner, TableColumn} from 'typeorm';
+
+export class ActivationPrefs1682636695021 implements MigrationInterface {
+  public async up(queryRunner: QueryRunner): Promise<any> {
+      await queryRunner.addColumn('activations', new TableColumn({
+        name: 'prefs',
+        type: nativeValues.jsonType,
+        isNullable: true,
+      }));
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<any> {
+    await queryRunner.dropColumn('activations', 'prefs');
+  }
+}