Add option to be notified when a followed user posts (#13546)

* Add bell button

Fix #4890

* Remove duplicate type from post-deployment migration

* Fix legacy class type mappings

* Improve query performance with better index

* Fix validation

* Remove redundant index from notifications

app/javascript/mastodon/features/account_timeline/components/header.js

@@ -55,6 +55,10 @@ export default class Header extends ImmutablePureComponent {
     this.props.onReblogToggle(this.props.account);
   }
 
+  handleNotifyToggle = () => {
+    this.props.onNotifyToggle(this.props.account);
+  }
+
   handleMute = () => {
     this.props.onMute(this.props.account);
   }
@@ -106,6 +110,7 @@ export default class Header extends ImmutablePureComponent {
           onMention={this.handleMention}
           onDirect={this.handleDirect}
           onReblogToggle={this.handleReblogToggle}
+          onNotifyToggle={this.handleNotifyToggle}
           onReport={this.handleReport}
           onMute={this.handleMute}
           onBlockDomain={this.handleBlockDomain}