(core) run survey for new users only when a survey doc is set

Summary:
stop providing a default document id DOC_ID_NEW_USER_INFO for
surveying, and don't show survey if a document id is not available.

Test Plan: existing tests pass; grist-core checked

Reviewers: georgegevoian

Reviewed By: georgegevoian

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3225

app/server/lib/FlexServer.ts

@@ -76,8 +76,9 @@ const HEALTH_CHECK_LOG_SHOW_FIRST_N = 10;
 // And we show every Nth health check:
 const HEALTH_CHECK_LOG_SHOW_EVERY_N = 100;
 
-// DocID of Grist doc to collect the Welcome questionnaire responses.
-const DOC_ID_NEW_USER_INFO = process.env.DOC_ID_NEW_USER_INFO || 'GristNewUserInfo';
+// DocID of Grist doc to collect the Welcome questionnaire responses, such
+// as "GristNewUserInfo".
+const DOC_ID_NEW_USER_INFO = process.env.DOC_ID_NEW_USER_INFO;
 
 export interface FlexServerOptions {
   dataDir?: string;
@@ -1593,6 +1594,8 @@ export class FlexServer implements GristServer {
 
   private async _recordNewUserInfo(row: object) {
     const urlId = DOC_ID_NEW_USER_INFO;
+    // If nowhere to record data, return immediately.
+    if (!urlId) { return; }
     let body: string|undefined;
     let permitKey: string|undefined;
     try {

app/server/lib/sendAppPage.ts

@@ -46,6 +46,7 @@ export function makeGristConfig(homeUrl: string|null, extra: Partial<GristLoadCo
     maxUploadSizeAttachment: (Number(process.env.GRIST_MAX_UPLOAD_ATTACHMENT_MB) * 1024 * 1024) || undefined,
     timestampMs: Date.now(),
     enableWidgetRepository: Boolean(process.env.GRIST_WIDGET_LIST_URL),
+    survey: Boolean(process.env.DOC_ID_NEW_USER_INFO),
     ...extra,
   };
 }