title: Prometheus alertmanager send notifications to multiple slack channel
body: <p>We have two different teams working on different applications.I would like send alert notifications to different slack channels via using same alerts expressions. I found some examples but not understand what is the main reason to use <code>receiver: 'default'</code> when try to add new route? What is the role of this and what if it affects if ı change this?</p>
  <p>Meanwhile will be appreciate if you can help how should I send the notifations to multiple slack channels.. New one is what I tried.</p>
  <p>Current alertmanager.yml</p>
  <pre><code>receivers:
    - name: 'team-1'
      slack_configs:
      - api_url: 'https://hooks.slack.com/services/1'
        channel: '#hub-alerts'
  route:
    group_wait: 10s
    group_interval: 5m
    receiver: 'team-1'
    repeat_interval: 1h
    group_by: [datacenter]
  </code></pre>
  <hr />
  <p>New  alertmanager.yml</p>
  <pre><code>alertmanager.yml:
      receivers:
        - name: 'team-1'
          slack_configs:
          - api_url: 'https://hooks.slack.com/services/1'
            channel: '#channel-1'
            send_resolved: true
        
        - name: 'team-2'
          slack_configs:
          - api_url: 'https://hooks.slack.com/services/2'
            channel: '#channel-2'
            send_resolved: true
  
  route:
    group_wait: 10s
    group_interval: 5m
    repeat_interval: 1h
    group_by: [datacenter]
    receiver: 'default'
    routes:
    - receiver: 'team-1'
    - receiver: 'team-2'
  </code></pre>
  <hr />