website/docs/r/emr_cluster: Update documentation for bid_price
website/docs/r/emr_cluster: Update documentation for bid_price

Closes: #8153

The attribute bid_price is allowed for the Master instance group since a
master node can be either a spot instance or an onDemand instance.

terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws