[FEATURE REQUEST] Possibility to define multiple times same alerting type

[philippe-granet]

I have to publish alerts to differents Mattermost channels.
Configuration could be like this:

alerting:
  mattermost1:
    type: mattermost
    webhook-url: "http://**********/hooks/webhook1"
  mattermost2:
    type: mattermost
    webhook-url: "http://**********/hooks/webhook2"

endpoints:
  - name: website1
    url: "https://twin.sh/health"
    alerts:
      - name: mattermost1
        enabled: true
  - name: website2
    url: "https://github.com/TwiN/gatus"
    alerts:
      - name: mattermost2
        enabled: true

[TwiN]

Duplicate of #96
React with 👍 on the issue above to increase the odds that I'll implement it.

In the mean time, you could try using pings in the alert description to bring the attention of specific groups to specific alerts.