Restore onboarding modal (#6303)

* Restore onboarding modal
Revert 5ba8b3a396895ecec083c5258aaf9084d584a7c4

* Change greeting elephant graphic, fix up some design issues

* Fix wrong link color in onboarding modal

app/javascript/mastodon/features/ui/components/modal_root.js

@@ -9,6 +9,7 @@ import VideoModal from './video_modal';
 import BoostModal from './boost_modal';
 import ConfirmationModal from './confirmation_modal';
 import {
+  OnboardingModal,
   MuteModal,
   ReportModal,
   EmbedModal,
@@ -17,6 +18,7 @@ import {
 
 const MODAL_COMPONENTS = {
   'MEDIA': () => Promise.resolve({ default: MediaModal }),
+  'ONBOARDING': OnboardingModal,
   'VIDEO': () => Promise.resolve({ default: VideoModal }),
   'BOOST': () => Promise.resolve({ default: BoostModal }),
   'CONFIRM': () => Promise.resolve({ default: ConfirmationModal }),