[datadog_powerpacks] Implement support for live span and more widgets

[dashashifrina]

This pull request implements the second part of the support for the powerpack resource in Terraform.

Previous PR:

• [datadog_powerpacks] Implement support for basic widgets #2157

Changes

• Add support for setting live_span in powerpack. In regular dashboard widgets, live_span is set at the widget level NOT resource level. For example, event_stream and trace_service widgets use live_span, within a powerpack, we set live_span under the group_widget object instead. With these changes, users will be redirected to set a live_span property at the powerpack resource level if they attempt to set it at the widget level.
• Add support for widgets with request LIST property (note: there are some widgets that define request as a single value and will be handled in a follow up)
• Add support for widgets with custom_link LIST property
• Add support for:
  • alert_value
  • change
  • event_stream
  • event_timeline
  • manage_status
  • query_value
  • toplist
  • trace_service
• Add test and recorded cassettes for all the widgets listed above.
• Add doc.

How to test:

1. Build the provider locally.
2. Try this powerpack resource with all the supported widgets:

resource "datadog_powerpack" "foo2" {
    name = "Sample Powerpack"
    tags = ["tag:foo1", "tag:foo2"]
    description = "Test Powerpack 2"

  template_variables {
    defaults = ["defaults"]
    name     = "datacenter"
  }
  widget {
    alert_value_definition {
	    alert_id = "895605"
    }
  }
  widget {
    alert_value_definition {
	    alert_id = "895606"
	    precision = 1
	    unit = "b"
	    title_size = "16"
	    title_align = "center"
	    title = "Widget Title"
	    text_align = "center"
    }
  }
   widget {
      change_definition {
		      request {
	      q             = "avg:system.load.1{env:staging} by {account}"
	      change_type   = "absolute"
	      compare_to    = "week_before"
	      increase_good = true
	      order_by      = "name"
	      order_dir     = "desc"
	      show_present  = false
		      }
		      title     = "Widget Title"
      }
   }
  widget {
    event_stream_definition {
      query       = "*"
      event_size  = "l"
      title       = "Widget Title"
      title_size  = 16
      title_align = "right"
    }
  }
  widget {
    manage_status_definition {
	    sort = "triggered,desc"
	    title_size = "20"
	    title = ""
	    title_align = "center"
	    hide_zero_counts = true
	    summary_type = "combined"
	    color_preference = "background"
	    query = "env:prod group_status:alert"
	    show_last_triggered = true
	    display_format = "countsAndList"
    }
    widget_layout {
	    height = 6
	    width = 4
	    x = 5
	    y = 5
    }
  }
  widget {
    trace_service_definition {
      display_format     = "three_column"
      env                = "datadog.com"
      service            = "alerting-cassandra"
      show_breakdown     = true
      show_distribution  = true
      show_errors        = true
      show_hits          = true
      show_latency       = false
      show_resource_list = false
      size_format        = "large"
      span_name          = "cassandra.query"
      title              = "alerting-cassandra #env:datadog.com"
      title_align        = "center"
      title_size         = "13"
    }
  }
  widget {
    event_timeline_definition {
      title = "Widget Title"
      title_align = "right"
      title_size = "16"
      tags_execution = "and"
      query = "status:error"
    }
    widget_layout {
      height = 4
      width = 3
      x = 5
      y = 5
    }
  }
  widget {
    query_value_definition {
      request {
        q          = "avg:system.load.1{env:staging} by {account}"
        aggregator = "sum"
        conditional_formats {
          comparator = "<"
          value      = "2"
          palette    = "white_on_green"
        }
        conditional_formats {
          comparator = ">"
          value      = "2.2"
          palette    = "white_on_red"
        }
      }
      autoscale   = true
      custom_unit = "xx"
      precision   = "4"
      text_align  = "right"
      title       = "Widget Title"
    }
  }
  widget {
    toplist_definition {
      request {
        q = "avg:system.cpu.user{app:general} by {datacenter}"
        conditional_formats {
          comparator = "<"
          value      = "2"
          palette    = "white_on_green"
        }
        conditional_formats {
          comparator = ">"
          value      = "2.2"
          palette    = "white_on_red"
        }
      }
      title = "Widget Title"
    }
  }
}

[woodb]

lgtm!

The base branch was changed.