(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/client/ui/DocMenu.ts

@@ -174,7 +174,14 @@ function createLoadedDocMenu(owner: IDisposableOwner, home: HomeModel) {
       testId('doclist')
     ),
     dom.maybe(use => !use(isNarrowScreenObs()) && ['all', 'workspace'].includes(use(home.currentPage)),
-              () => upgradeButton.showUpgradeCard(css.upgradeCard.cls(''))),
+      () => {
+        // TODO: These don't currently clash (grist-core stubs the upgradeButton), but a way to
+        // manage card popups will be needed if more are added later.
+        return [
+          upgradeButton.showUpgradeCard(css.upgradeCard.cls('')),
+          home.app.supportGristNudge.showCard(),
+        ];
+      }),
   ));
 }