[datadog_logs_custom_destination] Introduce logs custom destination resource

[Prepager]

Following the release of the Logs Custom Destinations Public API, we want to provide a Terraform resource for it

Example usage

resource "datadog_logs_custom_destination" "http_basic_auth" {
  name                               = "http basic"
  query                              = "source:dummy"
  forward_tags                       = false
  forward_tags_restriction_list      = ["a", "b"]
  forward_tags_restriction_list_type = "ALLOW_LIST"

  http_destination {
    endpoint = "https://example.org"
    basic_auth {
      username = "username"
      password = "password"
    }
  }
}