Feature Request: allow "custom_template_format" to be specified

[lucas-leanix]

Describe the issue

When creating an alert we can describe both custom_summary and custom_description, but the field "custom_template_format" is defaulted to HTML. I would like to be able to declare this field, in order to create "MARKDOWN" alert notifications like it's possible in the UI.

Configuration

resources:
  alerts:
    testAlert:
      evaluation:
        comparison_operator: "IS_NOT_NULL"
        empty_result_state: "OK"
        source:
          name: Field
        notification:
          notify_on_ok: false
          retrigger_seconds: 1
          subscriptions:
            - destination_id: destinationId
      schedule:
        quartz_cron_schedule: 0 50 8 ? * *
      display_name: "Name"
      custom_summary: "Name"
      custom_description: "Markdown description.\n\n@QUERY_RESULT_TABLE"
      # custom_template_format: "MARKDOWN" This field is not available
      query_text: >
        select * from test;

OS and CLI version

v1.7.0