(core) Add optional telemetry to grist-core

Summary:
Adds support for optional telemetry to grist-core.

A new environment variable, GRIST_TELEMETRY_LEVEL, controls the level of telemetry collected.

Test Plan: Server and unit tests.

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: dsagal, anaisconce

Differential Revision: https://phab.getgrist.com/D3880

app/server/generateInitialDocSql.ts

@@ -3,6 +3,7 @@ import { create } from 'app/server/lib/create';
 import { DocManager } from 'app/server/lib/DocManager';
 import { makeExceptionalDocSession } from 'app/server/lib/DocSession';
 import { DocStorageManager } from 'app/server/lib/DocStorageManager';
+import { createDummyTelemetry } from 'app/server/lib/GristServer';
 import { PluginManager } from 'app/server/lib/PluginManager';
 
 import * as childProcess from 'child_process';
@@ -33,7 +34,7 @@ export async function main(baseName: string) {
     }
     const docManager = new DocManager(storageManager, pluginManager, null as any, {
       create,
-      getTelemetryManager: () => undefined,
+      getTelemetry() { return createDummyTelemetry(); },
     } as any);
     const activeDoc = new ActiveDoc(docManager, baseName);
     const session = makeExceptionalDocSession('nascent');