(core) Limit related videos when playing onboarding video tour from home page

Summary:
When video is opened from the app homepage, it opens in a popup, which stays
open when it ends. The rel=0 parameter limits the related videos shown at the
end to those from the same channel, avoiding surprising unrelated videos.

This doesn't affect the video shown during initial onboarding, since that once
auto-closes when it ends.

Test Plan: Tested manually

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D4313

app/client/ui/OpenVideoTour.ts

@@ -26,6 +26,9 @@ const testId = makeTestId('test-video-tour-');
           height: '100%',
           width: '100%',
           origin: getMainOrgUrl(),
+          playerVars: {
+            rel: 0,
+          },
         },
         cssYouTubePlayer.cls(''),
       );

app/client/ui/YouTubePlayer.ts

@@ -29,6 +29,7 @@ export interface PlayerVars {
   fs?: 0 | 1;
   iv_load_policy?: 1 | 3;
   modestbranding?: 0 | 1;
+  rel?: 0 | 1;
 }
 
 export interface PlayerStateChangeEvent {