RHCS4 - ceph-ansible - add additional custom endpoint for alertmanager

Issue

How to add second endpoint for alertmanager, additional to default one.
- example of expected alertmanager.yml

route:
  group_by: ['alertname']
  group_wait: 10s
  group_interval: 10s
  repeat_interval: 1h
  receiver: 'ceph-dashboard'
  continue: true
  receiver: 'your-custom-endpoint'

receivers:
- name: 'ceph-dashboard'
  ..leave as is
- name: 'your-custom-endpoint'
  webhook_configs:
  - whatever you like