Add "dismiss_all" function to persistent_notification service

Feature Requests
1

Due to an automation bug, I created over 1,000 persistent notifications. I’d love to see a “dismiss_all” function in persistent_notification service.

For the record, I “solved” my issue by using the template dev tool to create a script sequence:

dismiss_all:
  sequence:
{%- for item in states.persistent_notification %}
  - data:
      notification_id: {{ item.entity_id|replace("persistent_notification.","") }}
    service: persistent_notification.dismiss
{% endfor %}