Add question link to the 'stopped working' email template. (#19815)

* Add question link to the 'stopped working' email template.

* Adjusted copy from alert email to correctly indicate how to unsubscribe

src/metabase/email/alert_stopped_working.mustache

 {{> metabase/email/_header }}
-    <p>Alerts about {{questionName}} have stopped because {{deletionCause}}.</p>
+    <p>Alerts about <a href="{{questionURL}}">{{questionName}}</a> have stopped because {{deletionCause}}.</p>
 {{> metabase/email/_footer}}

src/metabase/email/alert_you_were_added.mustache

 {{> metabase/email/_header }}
     <p>You’re now getting alerts about <a href="{{questionURL}}">{{questionName}}</a>.</p>
     <p>We’ll send you an email {{alertCondition}}.</p>
-    <p>If you don’t want to receive these alerts, you can <a href="{{questionURL}}">go to this question</a> and unsubscribe from the menu in the top-right.</p>
+    <p>If you don’t want to receive these alerts, you can <a href="{{questionURL}}">go to this question</a> and unsubscribe by clicking the bell icon on the bottom right.</p>
 {{> metabase/email/_footer}}