Add column revamp properties to dashboard log stream

[Prepager]

This PR adds four new properties to the dashboard log stream schema originating from the column revamp: show_date_column, show_message_column, message_display, and sort.

From: zorkian/go-datadog-api#321 DataDog/datadog-api-client-go@4f430b2

[jbenais]

Good for Dashboards, thank you! 💯
Would it just be possible to update the tests with the new properties?

[gzussa]

Thanks! One type should be changed. Also we don't use the zorkian client anymore but this https://github.com/DataDog/datadog-api-client-go

[nmuesch]

Thanks for the work on this @Prepager!! Could you also add these fields to the docs page here - https://github.com/terraform-providers/terraform-provider-datadog/blob/master/website/docs/r/dashboard.html.markdown under log_stream_definition and the example config?

[gzussa]

This seems great! Thanks!!