(core) Add document usage banners

Summary:
This also enables the new Usage section for all sites. Currently,
it shows metrics for document row count, but only if the user
has full document read access. Otherwise, a message about
insufficient access is shown.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Subscribers: alexmojaki

Differential Revision: https://phab.getgrist.com/D3377

app/client/ui/AppUI.ts

@@ -1,3 +1,4 @@
+import {DocUsageBanner} from 'app/client/components/DocUsageBanner';
 import {domAsync} from 'app/client/lib/domAsync';
 import {loadBillingPage} from 'app/client/lib/imports';
 import {createSessionObs, isBoolean, isNumber} from 'app/client/lib/sessionObs';
@@ -149,6 +150,7 @@ function pagePanelsDoc(owner: IDisposableOwner, appModel: AppModel, appObj: App)
     contentMain: dom.maybe(pageModel.gristDoc, (gristDoc) => gristDoc.buildDom()),
     onResize,
     testId,
-    contentBottom: dom.create(createBottomBarDoc, pageModel, leftPanelOpen, rightPanelOpen)
+    contentTop: dom.create(DocUsageBanner, pageModel),
+    contentBottom: dom.create(createBottomBarDoc, pageModel, leftPanelOpen, rightPanelOpen),
   });
 }