[WIP] Cron monitors

[cysp]

👋 this is not ready for real review, though the api response implementation is complete enough to successfully read an imported resource.

I'm posting this for early guidance and feedback on the proposed resource schema, in particular the complex configuration sub-object (and also general code organisation and implementation).

A cron monitor resource defined using this schema would look like this:

resource "sentry_monitor" "this" {
  organization = var.sentry_org

  project = var.sentry_project_slug
  type    = "cron_job"
  name    = "My cool cron monitor"
  slug    = "my-cool-cron-monitor"

  status   = "active"
  is_muted = true

  config = {
    alert_rule_id           = null
    checkin_margin          = 30
    failure_issue_threshold = null
    max_runtime             = 360
    recovery_threshold      = null
    # schedule_crontab        = "0 0 * * *"
    schedule_interval = {
      # year    = null
      # month   = null
      # week = null
      day  = 1
      # weekday = null
      # hour = null
      # minute  = null
    }
    timezone = "UTC"
  }
}

[cysp]

@jianyuan 👋 any thoughts on this schema design (and partial implementation)?