(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/server/lib/requestUtils.ts

@@ -2,7 +2,7 @@ import {ApiError} from 'app/common/ApiError';
 import {DEFAULT_HOME_SUBDOMAIN, isOrgInPathOnly, parseSubdomain, sanitizePathTail} from 'app/common/gristUrls';
 import * as gutil from 'app/common/gutil';
 import {DocScope, QueryResult, Scope} from 'app/gen-server/lib/HomeDBManager';
-import {getUserId, RequestWithLogin} from 'app/server/lib/Authorizer';
+import {getUser, getUserId, RequestWithLogin} from 'app/server/lib/Authorizer';
 import {RequestWithOrg} from 'app/server/lib/extractOrg';
 import {RequestWithGrist} from 'app/server/lib/GristServer';
 import log from 'app/server/lib/log';
@@ -352,3 +352,9 @@ export function addAbortHandler(req: Request, res: Writable, op: () => void) {
     }
   });
 }
+
+export function isDefaultUser(req: Request) {
+  const defaultEmail = process.env.GRIST_DEFAULT_EMAIL;
+  const {loginEmail} = getUser(req);
+  return defaultEmail && defaultEmail === loginEmail;
+}