(core) Update HelpScout beacon to work with embedded documentation articles.

Summary:
- Fix base href in HelpScout beacon when showing articles (in particular for Firefox)
- Show the 'Answers' tab normally except when reporting an error.
- Combine the "Give Feedback" and "Help Center" buttons into one that normally
  opens the beacon (with a link to Help Center and to Community Forum), and a
  smaller one that opens the Help Center site in a new tab.
- Update HELP_SCOUT_* env vars to use _V2 suffix, to allow them to coexist with
  code using the previous beacon.

Test Plan: Updated the browser test to check the new behavior.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3170

app/client/ui/NotifyUI.ts

@@ -145,7 +145,7 @@ function buildNotifyDropdown(ctl: IOpenController, notifier: Notifier, appModel:
         cssDropdownFeedbackLink(
           cssDropdownFeedbackIcon('Feedback'),
           'Give feedback',
-          dom.on('click', () => beaconOpenMessage({appModel, onOpen: () => ctl.close()})),
+          dom.on('click', () => beaconOpenMessage({appModel, onOpen: () => ctl.close(), route: '/ask/message/'})),
           testId('feedback'),
         )
       ),