provider/atlas: Add a Atlas Artifact Data Source (#7419)
provider/atlas: Add a Atlas Artifact Data Source (#7419)

* small doc update

* provider/atlas: Add docs for Artifact Data Source

* provider/atlas: Remove a test method that isn't used

* provider/atlas: Add Data Source for Atlas Artifact

* provider/atlas: Show deprecation error on atlas_artifact resource

charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,ashinohara/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,ashinohara/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,nbaztec/terraform-provider-aws,nbaztec/terraform-provider-aws,ashinohara/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,ClementCunin/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,nbaztec/terraform-provider-aws,Ninir/terraform-provider-aws,ashinohara/terraform-provider-aws,nbaztec/terraform-provider-aws